An Evaluation of Past and Present Water Quality Conditions in Bear Lake, Waupaca County, Wisconsin

R. Cramlet and N. Turyk

Center for Watershed Science and Education

University of Wisconsin-Stevens Point

May 2002

Final Report to the

Wisconsin Department of Natural Resources

Executive Summary Water quality concerns regarding Bear Lake, Waupaca County, Wisconsin have

prompted this study of the physical, chemical and biological characteristics of the lake,

the groundwater feeding it, and its watershed. Some of the local residents have perceived

an increase in aquatic plants over the years and the State of the Wolf Basin (DNR, 2001)

has characterized Bear Lake as being sensitive to phosphorous loading and having poor

water quality due to some algae blooms and somewhat excessive plant growth.

This study was conducted beginning in the spring of 2001 to evaluate current

water quality conditions in Bear Lake. The study consisted of lake and stream water

quality monitoring, a shallow groundwater assessment, an aquatic plant survey,

delineation of groundwater and surface watersheds, and a survey of the residents living

within the Bear Lake watershed. We met with the Bear Lake Association and watershed

citizens before the study to discuss study design and again at the end to share the results.

In addition to a current “State of Bear Lake”, the results of this study were

compared to the results of a study conducted in the late 70’s and early 80’s to determine

if noticeable changes are occurring within the lake and to guide lake management

decisions. Depleted dissolved oxygen concentrations continue to be a concern. Much of

the lake (below 20 feet deep) has dissolved oxygen concentrations that are below 1 mg/L

during the summer growing season. These are conditions that are uninhabitable by most

aquatic organisms. These oxygen conditions are related to nutrients (predominantly

phosphorus) that entered the lake over time. The sources of the nutrients are from within

the watershed as well as local shoreland practices and uses.

Results of the current study, when compared to the 1980s data, show several

changes. Secchi disk readings, which measure water clarity, have improved since the late

1970’s and early 1980’s. Chlorophyll a (a measure of algae) has also shown a great

improvement over the past twenty-five years. Nutrient concentrations appear to have

remained fairly constant in the hypolimnion (bottom) of the lake. This continuity is not

surprising, as once phosphorus enters a lake, it begins to cycle within the system and

removal is difficult and takes a considerable amount of time.

Over time the reduction of new nutrient inputs to the lake should improve the

lake’s water quality. This nutrient reduction should take place on both a local and

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watershed scale. The citizen survey revealed that 95% of the respondents use lawn

and/or garden fertilizer. Efforts to reduce/eliminate the use of fertilizers should be made.

Other near-lake recommendations include recreating riparian buffers to reduce sediments

and nutrient movement to the lake and provide habitat for the majority of lake species

that require near-shore habitat as part of their life cycle.

Much of the shallow groundwater flowing into Bear Lake is impacted from local

and/or wetland influences. Approximately 20% of the shallow groundwater sites that

were sampled appear to be influenced by septic system impacts. Efforts should be made

to site future systems as far from the lake as possible, particularly in areas identified as

groundwater inflow in this study.

In the watershed the use of best management practices can help to reduce

agricultural sources of nutrient inputs to Bear Lake. These practices include (but are not

limited to) nutrient management, cover crops, crop rotations, fencing animals from

streams, maintaining vegetative cover in pastures, controlling and properly land

spreading animal waste, and utilizing buffers near wetlands, steam corridors, and the

lake.

The diversity of aquatic plants in Bear Lake is about average for a developed lake

in this part of Wisconsin. Most of the plants that are present are tolerant of disturbance

and some can coexist well with light-limited conditions produced by algae blooms.

Eurasian milfoil was identified in the aquatic plant survey. This exotic species was

concentrated in a small area on the north end of the lake. Prompt action is necessary to

control the spread of this exotic species.

It is important for individuals that live within the Bear Lake watershed to

acknowledge their role in protecting the lake. Information about Bear Lake is available

and should be utilized to develop a lake/watershed management plan. This plan should

identify a vision for the lake, goals for the lake water and habitat quality, and identify

options for obtaining these goals. Ideally the plan should be constructed using input from

the Lake Association members, watershed citizens and businesses, county and university

personnel, Department of Natural Resources, and others.

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ACKNOWLEDGEMENTS

Many individuals made the execution and success of this project possible. The

Wisconsin Department of Natural Resources, the Bear Lake Association, the Waupaca

County Water Quality Fund, and the University of Wisconsin Stevens Point

Environmental Task Force Program provided funding for this study.

I would like to thank the following people for their assistance and support

throughout the project:

Nancy Turyk for her assistance in the field sampling and especially for her insight

and knowledge throughout the project and the writing of the final report.

Richard Stephens, Jim Licari and Kandace Waldmann for coordinating the

analysis of the water, plant, and sediment samples collected.

Stacey Allen for conducting the aquatic plant study.

The students associated with the Environmental Task Force Program who

performed laboratory analysis on many of the water samples and assisted in fieldwork.

Kevin Lawton for his assistance with GIS.

Jeff Stelzer, Tracy Malkovich, Amy Dechamps, Clint Otto, Adam Freihoefer, and

many others who helped in the collection of data and made this project possible.

Sue Ann Goedderz and her family for their support and cooperation throughout

the project, gathering, distributing and summarizing the survey of land owners and the

use of their boat.

Jim Cauley and his wife for their support, cooperation and desire to learn more

about Bear Lake.

Dwayne Abramson for his support, cooperation and providing historical

knowledge of the lake.

The Bear Lake Campground for their interest and cooperation throughout the

project, and for the use of their boat.

The Bear Lake Association for their interest and desire to learn more about the

lake.

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TABLE OF CONTENTS

EXECUTIVE SUMMARY ......................................................................................2

LIST OF FIGURES ...............................................................................................7

LIST OF TABLES.................................................................................................9

LIST OF APPENDICES........................................................................................9

INTRODUCTION ................................................................................................10

Description of Study Area.............................................................................................. 10

METHODS..........................................................................................................14

Stream Flow..................................................................................................................... 14

Mid-Lake Chemistry ...................................................................................................... 16

Groundwater Study ........................................................................................................ 17

Interstitial Water, Aquatic Macrophyte, and Sediment Study................................... 20

PHYSICAL SETTING .........................................................................................23

Topography ..................................................................................................................... 23

Geology............................................................................................................................. 23

Soils................................................................................................................................... 25

RESULTS AND DISCUSSION ...........................................................................30

Bear Lake Citizen Survey .............................................................................................. 30

WATER QUALITY........................................................................................................ 33

Stream flow...................................................................................................................... 33

Mid-lake Water Quality Data ........................................................................................ 34 Dissolved Oxygen and Temperature............................................................................. 34 Secchi Depth and Chlorophyll a ................................................................................... 38

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Conductivity, Alkalinity, Total Hardness, pH .............................................................. 41 Total Phosphorus (TP) .................................................................................................. 43 Nitrogen ........................................................................................................................ 45

Sediment, Macrophyte, and Interstitial Water Study ................................................. 52

Groundwater Study ........................................................................................................ 56

Trophic Status Index ...................................................................................................... 65

Aquatic Macrophyte Survey (S. Allen) ......................................................................... 69

2001 BEAR LAKE AQUATIC PLANT SURVEY ................................................71

Methodology .................................................................................................................... 71

Bear lake Aquatic Plant Species .................................................................................... 72 Floating leaf Species ..................................................................................................... 72 Submergent Species ...................................................................................................... 72

Total Occurrence ............................................................................................................ 75

Percent Frequency .......................................................................................................... 76

Simpson’s Diversity ........................................................................................................ 76

Mean Density................................................................................................................... 78

Dominance Value ............................................................................................................ 78

Discussion (S. Nichols, WGNHS and S. Allen)............................................................. 79

WISCONSIN LAKES MODELING SUITE (WILMS) (AMY DECHAMPS AND PAUL MCGINLEY) .............................................................................................80

Background ..................................................................................................................... 80

Hydrology ........................................................................................................................ 80

Phosphorus ...................................................................................................................... 82

In-Lake Phosphorus Concentration Modeling............................................................. 83

Uncertainty ...................................................................................................................... 85

CONCLUSIONS/RECOMMENDATIONS ...........................................................86

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APPENDICES.....................................................................................................88

LIST OF FIGURES Figure 1. Surface water watershed of Bear Lake, Waupaca Co., .................................... 12 Figure 2. Groundwater watershed of Bear Lake, Waupaca County, Wisconsin. ............ 12 Figure 3. Map of stream gauging sites and the mid-lake sample site. ............................. 15 Figure 4. Location of mini-piezometer sampling sites around Bear Lake....................... 19 Figure 5. Diagram showing determination of groundwater up-welling, down-welling and

no-welling using mini-piezometers........................................................................... 20 Figure 6. Map of interstitial water, sediment, and aquatic macrophyte collection sites

around Bear Lake, which also correspond with the aquatic plant survey sites......... 21 Figure 7. Diagram of interstitial water sampling device.................................................. 22 Figure 8. Topography map of the Bear Lake Area, Waupaca Co., WI. .......................... 24 Figure 9. General Soils Map of the Lower Little Wolf Watershed, Waupaca County,

Wisconsin.................................................................................................................. 26 Figure 10. Land use map of the Bear Lake surface water watershed, Waupaca Co., WI.28 Figure 11. Land use within the Bear Lake ground water watershed, Waupaca Co., WI. 29 Figure 12. Percentage of survey respondents who use Bear Lake for recreational

activities. ................................................................................................................... 31 Figure 13. Percentage of survey respondents who own a boat. ....................................... 31 Figure 14. Use of fertilizers within the Bear Lake Watershed. ....................................... 33 Figure 15. Diagram of Lake Stratification....................................................................... 35 Figure 16. Temperature profile in Bear Lake during summer stratification and fall

turnover. .................................................................................................................... 36 Figure 17. Monthly dissolved oxygen profile in Bear Lake during summer stratification

and during fall turnover. ........................................................................................... 37 Figure 18. Graphs show relationship between Secchi depth, chlorophyll a concentrations,

and TP concentrations of the epilimnion of Bear Lake during the summer of 2001.39 Figure 19. Graphs show the relationship between epilimnion total phosphorus and

chlorophyll a concentrations in Bear Lake, Waupaca Co., WI, from 1980-1982. ... 40 Figure 20. Graph of the epilimnion and hypolimnion total phosphorus concentrations in

Bear Lake, Waupaca Co., WI, by month for each sample year. ............................... 45 Figure 21. Schematic showing various forms of nitrogen and its movement in the

environment. (University of Minnesota. 2002)....................................................... 47 Figure 22. Epilimnion and hypolimnion ammonium concentrations in Bear Lake by

month. ....................................................................................................................... 48 Figure 23. NO2 + NO3 concentrations by month in Bear Lake, Waupaca Co., WI.......... 49 Figure 24. Total Nitrogen concentrations by month in Bear Lake, Waupaca Co., WI..... 50 Figure 25. Epilimnion TKN concentrations by month in Bear Lake, Waupaca Co., WI.51 Figure 26. Shows that as the interstitial water reactive P concentration increases, the

percent biomass in the plant tissues increases. ......................................................... 55 Figure 27. Shallow groundwater inflow/outflow determined by mini-piezometers around

Bear Lake. ................................................................................................................. 57

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Figure 28. Map of mini-piezometer chloride concentrations around Bear Lake. ............ 61 Figure 29. Mini-piezometer ammonium concentrations around Bear Lake. ................... 62 Figure 30. Map of mini-piezometer reactive phosphorus concentrations around Bear

Lake........................................................................................................................... 63 Figure 31. Map of mini-piezometer NO2+NO3 concentrations around Bear Lake.......... 64 Figure 32. Aquatic plant species present in Bear Lake.................................................... 72 Figure 33. Diagram of the mean density of three species of aquatic plants in each depth

zone of Bear Lake. .................................................................................................... 78 Figure 34. Diagram of dominance values for aquatic plant species found in Bear Lake. 79

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LIST OF TABLES Table 1. Analytical methods and corresponding detection limits for ETF Lab............... 18 Table 2. Categorization of Hardness by mg/L of Calcium Carbonate (CaCO3)............. 42 Table 3. Sensitivity of Lakes to Acid Rain ...................................................................... 42 Table 4. 1980-82 and 2001 average summer Secchi depth, chlorophyll a concentrations,

weighted TP values with calculated WTSI equivalent values. ................................. 67 Table 5. Apparent water quality categories for Wisconsin lakes based on chlorophyll a

content, water clarity, and Total P concentrations.*................................................. 68 Table 6. Trophic classification of Wisconsin lakes based on chlorophyll a, water clarity

measurements, and total phosphorus values. (Adapted from Lillie and Mason, 1983.)................................................................................................................................... 69

Table 7. Frequency of Occurrence of aquatic plant species in each depth zone. ............ 73 Table 8. Table of Coefficient Conservatism for species found in Bear Lake.................. 74 Table 9. Table of Total occurrence for species found in Bear Lake................................ 75 Table 10. Table of percent frequency for species of aquatic plants in Bear Lake. .......... 76 Table 11. Table of total density of aquatic plant species found in Bear Lake. ................ 77 Table 12. Hydrologic and Phosphorus Load Summary ................................................... 84 Table 13. Calculated and Predicted Values ..................................................................... 85

LIST OF APPENDICES Appendix A ……………………………..………………………………………………88

Appendix B …………………………..…………………………………………………96

Appendix C ………………………...………………………………………………….106

Appendix D ……………………………………………………………………………121

Appendix E ……………………………………………………………………...…….123

Appendix F ……………………………………………………………………………124

Appendix G ……………………………………………………………………………138

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INTRODUCTION

Water quality concerns regarding Bear Lake, Waupaca County, Wisconsin have

prompted further study of the physical, chemical and biological characteristics of the lake

and the groundwater feeding it. Local residents have observed an increase in plants over

the years. The Wolf Basin team has characterized Bear Lake as being sensitive to

phosphorous loading and having poor water quality due to some algae blooms and

somewhat excessive plant growth. This study was initiated to assess Bear Lake and its

watershed and identify areas and practices that can reduce nutrient inputs to the lake.

Description of Study Area

Bear Lake is a 194-acre natural drainage lake with a maximum depth of 62 feet,

and is located just outside the town of Manawa, and in the townships of Little Wolf and

Royalton in Waupaca County, Wisconsin. It receives its water from groundwater inflow,

runoff, precipitation, and three streams, which converge in a wetland area and flow into

the southwest end of Bear Lake. Bear Lake drains into the Lower Little Wolf River and

is within the Wolf River Basin. Both residents and area visitors use Bear Lake for

recreation. The lake’s development includes 85 houses and a public campground on the

east side. It has one public boat landing and one public beach.

A lake management plan was produced for the Bear Lake Watershed in 1984

using water quality data collected in the late 1970’s and early 1980’s. The Bear Lake

Homeowners Association was interested in collecting water quality and plant information

to compare with the older data to determine if measurable changes are occurring in the

lake and to update management strategies. The Lower Little Wolf River watershed was

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designated in 1998 as an USDA-EQIP watershed and henceforth, has had some non-point

source issues addressed by the Waupaca County Land Conservation Department staff.

Some of their efforts have resulted in conservation tillage practices on over 300 acres and

the re-creation of wetlands within the Bear Lake Watershed .

The surface watershed (Figure 1) is approximately 2,725 acres and the

groundwater watershed is approximately 3,569 acres (Figure 2). The regional (deeper)

groundwater flow comes in from the southwest and flows out of the north-northeast end

of the lake. Due to the steep topography of the area, there is local groundwater inflow all

around the lake.

Objectives of this study were to:

•Determine the current quality of groundwater feeding Bear Lake, the surface water quality of Bear Lake, and long-term trends in surface water quality.

•Assess the land use practices within the surface and groundwater watersheds and how they are related to Bear Lake’s water quality.

•Quantify principle nutrient and water budget components through groundwater flow estimates, water quality measurements, and land use. Relate to surface water quality through lake response models.

•Survey the aquatic macrophytes within the lake and determine if exotic species are present.

•Survey the landowners within the watershed to determine their uses of the lake, perceptions of water and fishing quality, and changes that may have occurred, as well as household and land use practices that may effect lake water quality.

•Provide recommendations to update the 1984 management plan that can initiate steps toward future lake management decisions to maintain or improve the health of the Bear Lake ecosystem.

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Figure 1. Surface watershed of Bear Lake, Waupaca County, Wisconsin.

Figure 2. Groundwater watershed of Bear Lake, Waupaca County, Wisconsin.

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Methods Stream Flow

Stream flow was measured at the Bear Lake inflows and outflow bi-monthly

during June through September of 2001 with a Marsh McBirney Model 2000 portable

flow meter, 100 ft. tape, and 2 chaining pins. The inflow consists of three streams, which

converge in a wetland area, so the inflow was gauged at the three separate streams along

Baldwin Road prior to convergence. A map displaying the locations of the stream

gauging sites can be found in Figure 3. Inflow 1 is located on the southwest side of the

intersection of Baldwin and Casey Lake Road. Inflow gauging site 2 is in a wooded

corridor on the south side of Baldwin Rd. west of inflow 1. Inflow gauging site 3 is

located where Spiegleberg Creek crosses Baldwin Rd., just south of the intersection of

Jake’s Rd. and Baldwin Rd. The outflow of Bear Lake was gauged on the south side of

North Water Dr. (4).

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Figure 3. Map of stream gauging sites and the mid-lake sample site.

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Mid-Lake Chemistry

Temperature and dissolved oxygen profiles, Secchi disk readings, and surface

conductivity readings were taken bi-monthly from June through September 2001, and

monthly in May, October, November, and January, at the mid-lake site. The mid-lake

site, the deepest area in the lake, is 62 feet deep, and was found by using an on-board

depth recorder. The site was described by using landmarks around the lake, and marked

with a Global Positioning System (GPS) (Figure 3).

Secchi disc readings were taken using a standard 8-inch diameter weighted disc.

The disc was lowered over the downwind, shaded side of the boat until it just disappeared

from sight and then raised until it was just visible. The mean of the two depths was

recorded. Surface conductivity was measured with a Mettler 126 conductivity meter.

Dissolved oxygen and temperature readings were taken using an YSI Model 50B

dissolved oxygen meter (Method 4500-06, APHA 1995). Readings were taken every two

feet starting at the surface and terminating at the lake bottom. The readings were used to

determine stratification and identify depths to take the water samples. Samples for

epilimnion, metalimnion, and hypolimnion were collected monthly from May through

November and once in February of 2002, using an alpha bottle. A preserved 125ml

bottle was prepared in the lab with 0.35mls of 1+1 H2SO4 per 125mls of sample and filled

in the field by transferring the sample from an unpreserved bottle to avoid loss of the

H2SO4. All samples that needed to be filtered were field filtered through an 42.5 mm in-

line filtering apparatus with a 60 ml syringe and 0.45 um membrane filters. Analyses

performed on the mid-lake samples include: nitrate and nitrite (NO2+NO3-(N)),

ammonium (NH4-(N)), Total Kjeldahl Nitrogen (TKN), Total phosphorus (TP), soluble

reactive phosphorus, chloride, pH, conductivity, alkalinity, total hardness, and

chlorophyll a.

Chlorophyll a samples were collected monthly from June through September.

Samples were collected near the surface as grab samples and field filtered using a 42.5

mm in-line filtering apparatus with a hand pump through 0.45 um membrane filters. The

filter was folded in half (chlorophyll a on the inside) and wrapped in aluminum foil and

transported back to the ETF lab on ice. One exception occurred on May 31st when the

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sample was transferred into a 1 liter polyethylene bottle and transported back to the lab

for filtering.

All samples were collected and transported on ice to the state certified

Environmental Task Force Lab (ETF) located at the University of Wisconsin-Stevens

Point. All lab analyses were completed using the methods described in Table 1.

Groundwater Study

Mini-piezometers were inserted into the lake bottom approximately every 200-

300 feet. Mini-piezometers were used to collect hydraulic head data at 69 sites around

Bear Lake in August 2001, using the Hvorslev slug test (Hvorslev, 1951). Each site was

thoroughly described and GPS readings were collected along with markings on a map

with site identification (Figure 4). Groundwater inflow areas occurred where the head

level in the mini-piezometer was above the lake surface and outflow areas occurred

where the head level in the mini-piezometer was below the lake surface (Figure 5).

Samples were collected from groundwater inflow (up-welling) areas.

Mini-piezometers were constructed from 5 foot length 4mm hollow

polypropylene tubing. At one end there is 2-inch screen that was made by using a small

diameter needle and sewing machine to allow the pore water to enter into the tubing,

completely separate from lake water. The end below the holes was melted closed and a 1

mL plastic pipette tip was attached to the end of the well for ease of insertion. A steel rod

was inserted into the mini-piezometer tube to make it rigid enough to be pushed into the

sediment. A steel tile probe initiated the hole before the well was introduced into the

ground. The tile probe was only used on sites where it became difficult to insert the well

due to the hard, compact substrate.

The mini-piezometers were inserted approximately 2 ft. into the sediment in

approximately 18 inches of water. Once the mini-piezometer was installed, a plastic

syringe was used to determine the hydraulic head relative to the lake water surface and to

extract a pore water sample from each site. Pore water was filtered through a 42.5 mm

in-line filtering apparatus with a 60 ml syringe through 934/AH (0.45 micron) membrane

filters and analyzed for NO2 + NO3 (N), ammonium, chloride, and reactive phosphorus.

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Table 1. Analytical methods and corresponding detection limits for ETF Lab.

ANALYSES

METHOD

METHOD DETECTION LIMIT

Alkalinity Titrimetric 2320 B

4 mg/L

Chloride Automated Ferricyanide 4500 C1 E

0.2 mg/L

Chlorophyll a Spectrometric 10200 H

0.1 mg/L

Color Spectrometric 2120

5 cu

Conductivity Conductivity Bridge 2510 B

0 umhos

Hardness, Calcium Titrimetric 3500 Ca D

4 mg/L

Hardness, Total Titrimetric 2340 C

4 mg/L

Nitrogen, Ammonia Automated Salicylate 4500-NH3 G

0.01 mg/L

Nitrogen, Nitrate + Nitrite Automated Cadmium Reduction 4500 NO3 F

0.021 mg/L

Nitrogen, Total Kjeldahl Block Digester; Auto Salicylate 4500-NH3 G

0.08 mg/L

pH Electrometric 4500 H B

0 mg/L

Phosphorus, Reactive Automated Colorimetric 4500 P F

0.003 mg/L

Phosphorus, Total Block Digester, Automated 4500 P F

0.012 mg/L

Potassium ICP 3120B

270 ug/L

Sodium ICP 3120B

2/46 ug/L

Sulfur (SO4) ICP 3120B

26 ug/L

Turbidity Nephelometric 2130 B

0.5 mg/L

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Figure 4. Location of mini-piezometer sampling sites around Bear Lake.

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Figure 5. Diagram showing determination of groundwater up-welling, down-welling and no-welling using mini-piezometers.

Water level in piezometer even with lake level: No flow (No-welling)

Water level in piezometer

below lake level: Groundwater

outflow (Down-welling)

Water level in piezometer

above lake level: Groundwater

inflow (Up-welling)

Lake Sediment

Interstitial Water, Aquatic Macrophyte, and Sediment Study

Sediment, aquatic macrophyte, and interstitial water samples were taken at twelve

sites around the lake (Figure 6), which site numbers corresponded with the aquatic plant

survey conducted by the ETF lab. A 1/8 meter square constructed of ¾” diameter PVC

tubing, was randomly dropped in about three feet of water at each of the 12 sites around

the lake. Aquatic macrophytes rooted within the PVC area were collected and

transported on ice to the ETF lab for analysis. Analyses for aquatic macrophytes include:

TKN and TP.

Interstitial water samples were taken using a 6-inch length of polyethylene

diffuser tubing (3/4 inch outside diameter) with a 1 inch Delrin tip. A ¼ inch threaded

rod was placed inside the diffuser tubing and a 1/8-inch outside diameter piece of Tygon

tubing was attached. The bottom of a 6”coffee can was also attached to the diffuser

tubing to prevent surface water infiltration into the sample. Figure 7 shows a diagram of

the interstitial water sampling device. The device was inserted into the sediment adjacent

to the disturbed area where aquatic macrophytes were collected, using a rigid steel rod

20

Figure 6. Map of interstitial water, sediment, and aquatic macrophyte collection sites around Bear Lake, which also correspond with the aquatic plant survey sites.

21

Figure 7. Diagram of interstitial water sampling device.

22

threaded to the rod inside the diffuser tubing. Sample was pulled up through the piece of

Tygon tubing with the use of a hand pump. The hand pump was attached to a side-arm

flask equipped with an in-line filter cassette containing a 0.45 micron and a 934 AH

47mm glass fiber filter. The first 20ml of sample was used to rinse the device, then the

analyzed sample was collected in a H2SO4 preserved bottle.

Sediment samples were taken from an undisturbed adjacent area to the aquatic

macrophyte and interstitial water samples. A hollow PVC pipe 2 inches in diameter, was

inserted approximately 6” into the sediment and a rubber stopper was inserted in the top

to create a suction to collect sediment from the lake bottom. The samples were collected

in plastic food grade bags and transported on ice back to the ETF lab for analysis. The

sediment samples were analyzed for NO2+NO3, ammonium, potassium, sulfate, reactive

phosphorus, total percent solids, and percent organic matter.

PHYSICAL SETTING

Topography

The topography of the Bear Lake watershed consists of rolling hills with gentle to

steep slopes interspersed with flat poorly drained basins (Figure 8). Areas of high relief

form the boundaries of the surface water watershed (Figure 1).

The topography of the northwestern and north-central portions of the watershed is

quite complex and is frequently pitted with kettles (depressions left by large, melting ice

blocks during the waning years of glaciation). Most of the kettles are filled with water to

form small ponds and Woodnorth and Fox Lakes. The topography of this area has been

further altered by sand and gravel mining operations.

Geology

The bedrock underlying the watershed consist of mostly Precambrian granites,

which are the oldest types of bedrock found in Wisconsin. Much of the younger,

overlying sandstone and limestone bedrock was eroded away in this area prior to the last

glacier. Glaciers further eroded the crystalline granite bedrock and considerably altered

the landscape. However, the major drainage valleys of the Wolf River remained

(Berkstresser 1964; Weidman and Schultz 1915).

23

Figure 8. Topography map of the Bear Lake Area, Waupaca Co., WI.

24

The surface geology of Waupaca County was largely determined by the Cary and

Valders stages of the Wisconsin Glacier. Massive ice movements and subsequent

melting resulted in the formation of hills, drumlins, kettles, drainage basins and their

surface deposits. The Bear Lake watershed is located near the border between Cary and

Valders deposits. These glacial drift deposits are composed of silt, sand, gravel, cobbles

and boulders that originally came from bedrock types to the north and east of Waupaca

County (Bushweiler, B. and Rasman, T. 1984.).

Soils

The soils found in Waupaca County have been derived primarily from the

weathering and transport of glacial drift deposits. Types of soils are classified according

to soil texture, structure, organic content, permeability and subsoils. The suitability of

soils for various uses will be determined by these properties as well as by slope of the

land and depth to bedrock or water table. Table 1 lists soil types, slopes, erosion

potential and some of the limitations and suitable uses for soils in the Bear Lake

watershed. A general soil map of the Waupaca County is presented in figure 9.

Dominant soil types can be divided into three groups: (I) Sandy loam and Loam Soils;

(II) Loamy Sand Soils; and (III) Organic muck soils.

Sandy loam and loam soils (Group I) have a yellow-brown to reddish-brown subsoil,

where they are well drained, covered by dark gray-brown topsoil. Their natural fertility

and good soil structure make these soils some of the best cropping soils in Waupaca

County. However, good land management practices are necessary to prevent excess

topsoil erosion particularly on slopes greater than 2%. Most of the Hortonville Loams on

slopes greater than 6% have already been severely eroded. Loam soils in the watershed

vary from excessively permeable, droughty soil to slowly permeable, wet soils depending

upon the quantity of sand, silt, or clay in the soils and the depth to groundwater.

Generally, sandy loam soils are found along drainage ways and in basins. Some of the

Group I soils are not suitable for septic systems because they percolate too quickly or are

too close to the water table.

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Loamy sand soils (Group II) have a higher percentage of sand than loam soils. These

soils are found along drainage ways and adjacent slopes. They are excessively permeable

and tend to be droughty on upland slopes or too wet in low-lying areas. Crop production

is slightly lower due to lower organic content and fertility. Erosion due to soil blowing is

also a problem. For these reasons, loamy sands are better suited to woodland or

Figure 9. General Soils Map of the Lower Little Wolf Watershed, Waupaca County, Wisconsin.

Bear Lake Watershed

pastureland than cropland. Good management practices are required on Group II soils to

prevent soil erosion from both water and wind and to maintain soil fertility. Group II

soils are also severely limited for proper septic system function because effluents drain

too rapidly through the soil and may contaminate the groundwater before proper

treatment can be achieved. Many homes along the south shore of Bear Lake are located

on these soils (Bushweiler, B. and Rasman, T. 1984.)

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Organic muck soils (Group III) can be found along drainage ways and in low lying

depressions in the watershed. These soils were formed from deposits of herbaceous

organic material under wet conditions and consist of black mucky peat and deep muck

over sandy subsoils. Muck soils are poorly drained and have a high available water

capacity. The water table is above or near the soil surface throughout much of the

growing season. These areas generally support marsh and wooded wetland vegetation.

They are considered to be unsuitable for most intensive land uses including cropland,

residential development and septic systems (Bushweiler, B. and Rasman, T. 1984.).

Land Use

GIS Coverage Data: ArcView GIS land coverage’s of Wisconsin were obtained by the Wisconsin Initiative for

Statewide Cooperation on landscape Analysis and Data (WDNR, WISCLAND). Land

cover data was derived from Landsat Thematic Mapper (TM) satellite imagery acquired

from fly-overs from 1991-1993. Specifically on the map, each pixel represents a 30

meter square, or 900 square meters on the ground.

Land use within the surface and ground water watershed plays an important role

in the water quality of aquatic ecosystem. According to the 1993 Wisconsin land use

cover map (WDNR, WISCLAND), nearly half (47%) of the surface water watershed, is

covered by agriculture. Forested land was the next predominant land use, covering

approximately 17% of the watershed. Wetland areas cover about 15% of the watershed,

while forested wetland areas cover approximately 8%. Open water (7%), grasslands

(5%) and barren land (3%) cover the remainder of the watershed. Figure 10 shows the

land use map of the Bear Lake surface water watershed.

Land use within the groundwater watershed is quite similar to the land use within

the surface water watershed. Agriculture covers nearly half of the groundwater

watershed, while forested land and wetlands are the next predominant land uses covering

approximately 15% each. Grasslands, forested wetlands, barren land and open water

cover the other 20% of the groundwater watershed. Figure 11 shows the land use map of

the Bear Lake groundwater watershed.

27

Figure 10. Land use map of the Bear Lake surface water watershed, Waupaca Co., WI.

28

Figure 11. Land use within the Bear Lake ground water watershed, Waupaca Co., WI.

29

RESULTS AND DISCUSSION

Bear Lake Citizen Survey

In our assessment of Bear Lake, it was desirable to identify the lake water quality

and recreational concerns of the people who use the lake. A survey questionnaire was

used to determine recreational uses of the lake, potential use conflicts, public perception

of water quality problems and the level of public interest in protecting the lake. In June

of 2001, the questionnaires were mailed or hand delivered to 276 residents in the

watershed, and 46 were returned; two of which were not completed but had comments

written on them. This was a 17% response, and approximately a 20% response is

considered to be average. A copy of the questionnaire and the hand written responses to

the questions are contained in (Appendix A).

Most of the respondents (75%) were lakeshore property owners. About one third

of the respondents who own or rent property on the lake, are year round residents. Range

of time living in the Bear Lake watershed was 1 to greater than 100 years. Ninety-one

percent of the respondents use the lake for some form of recreation. Recreational uses

are shown in Figure 12 and include: boating, fishing, picnicking, ice skating, hunting,

sail/wind surfing, snowmobiling, water-skiing, swimming, scenic view, hiking, cross

country skiing, entertaining, tubing, watching wildlife, and peace and quiet. Fishing and

swimming tied for the predominant uses, at 79%. Boating and aesthetics (enjoying the

natural scenic beauty) were also very popular among the respondents, both at 69%. Other

recreational uses, in declining order, include peace and quiet, entertaining, watch wildlife,

water skiing, ice-skating, picnicking, sail/wind surfing, hiking or cross-country skiing,

hunting and snowmobiling. Nearly 70% of the respondents owned a fishing boat, 38%

owned a paddleboat, 33% owned a pontoon boat, 21% owned a ski boat, 21% owned a

sail boat, and 7% owned a personal water craft (PWC) (Figure 13). The maximum

amount of marine gas used was 144 gallons per year used by one household and the

minimum was none. The average estimated amount of marine gas used per year was

found to be 21.4 gallons. The estimated total amount of marine gas used annually by

survey respondants on Bear Lake is 770 gallons.

30

Perception of water quality changes was mixed; over half of the respondents

(55%) felt that the water quality of Bear Lake has stayed the same. Thirty-two percent

felt that the water quality has declined, and 13% felt that the water quality has improved.

Septic system seepage (25%), herbicide/pesticide use (23 %), soil erosion (20%) and

fertilizer use (18%) were perceived by survey respondents to be the greatest contributors

to water quality decline.

Figure 12. Percentage of survey respondents who use Bear Lake for recreational activities.

0102030405060708090

Boatin

g

Picnick

ing

Ice Ska

ting

Huntin

g

Sail/W

ind-su

rfing

Fishing

Peace

and Q

uiet

Snowmob

iling

Watersk

iing

Swimming

Scenic

View

Enterta

ining

Watch W

ildlife

Hike/X-C

trySki

Perc

ent o

f Res

pond

ents

Figure 13. Percentage of survey respondents who own a boat.

0.0005.000

10.00015.00020.00025.00030.00035.000

Pontoo

n

Fishing Ski Sail

Jet S

ki

Paddle

Canoe

/Kayak

Perc

ent o

f Res

pond

ents

who

ow

n a

boat

31

The majority of the respondents (68%) felt that the fishing quality of Bear Lake

has stayed the same since they have fished on Bear Lake. Thirty-two percent felt that the

fishing quality has declined and there was not a single respondent who felt that the

fishing quality had improved. Just over half of the respondents felt that the fishing

quality of Bear Lake is good, while 21% feel that it is fair. Heavy recreational use (38%),

soil erosion (15%), and pesticide/herbicide use (15%) were perceived by survey

respondents to be the greatest contributors to fishing quality decline.

Nearly half of the respondents have a septic tank (45%), while 28% have a

drainage field, and 17% have a holding tank. The type, age, and quality of condition of

sewage disposal system, affects the nutrient loads entering the lake, however, even

properly functioning septic systems will release nutrients to the groundwater.

Just over half of the respondents use an automatic clothes washer, 35 % use a

dishwasher, and 12% of the respondents use a garbage disposal. Grounds up food from

garbage disposals contribute nutrients to the waste stream. Dishwasher detergents

contain phosphorus whereas other detergents purchased in Wisconsin do not. All of these

contribute heavier usage to one’s septic system, which may in turn contribute to the

nutrient load entering the lake.

Of the respondents, 95% use fertilizer and 5% do not use any type of fertilizer

(Figure 14). The majority of the respondents (75%) live on Bear Lake. Of these

respondents who live on the lake, 41% use fertilizers. Of the respondents who live on the

lake and use fertilizers, 86% use fertilizers on their lawn. This may affect the lake

directly by contributing excess nutrient runoff, which may enter the lake through surface

water runoff or via shallow groundwater flow. Efforts to reduce/eliminate the use of

fertilizers should be made within the surface and groundwater watershed.

Of the respondents who live within the Bear Lake watershed, only one-third use

fertilizers. This would have less impact to the lake due to a greater distance between the

fertilized area and the lake, and usually the distance between the fertilized area and the

water table is greater than those who live on the lake, however, it is still an input that

should be reduced and eliminated whenever possible.

32

Figure 14. Use of fertilizers within the Bear Lake Watershed.

Use of fertilizers within the Bear Lake watershed

USE FertilizersDo NOT use ferilizers

WATER QUALITY

Stream flow

Stream flow was measured 9 times throughout the study between June and

November. This information was used for the modeling portion of the project. The

inflow of Bear Lake consists of Spiegleberg Creek and two other intermittent streams,

which converge in a wetland area and flow into the lake. Flow was at a peak in June in

all of the streams, with the exception of inflow 3, which reached its peak flow in

September, but it was also near peak flow in June due to heavy rainfall. Dry conditions

reduced flow in inflows 1 and 2 to an immeasurable level in July. All stream flow data

are located in Appendix B, and figure 3 displays a map with stream gauging sites and the

mid-lake sample site.

Inflow 1 is located on the southwest corner of the intersection of Baldwin Rd. and

Casey Lake Rd. Discharge reached its maximum in mid-June at 0.96 cubic feet per

second due to heavy amounts rainfall in June. The average discharge between June and

November measured at this inflow was 0.18 cubic feet per second, the mean temperature

was 18.2oC, and the average conductivity was 504 umhos.

Inflow 2 is a wooded stream corridor, which passes under Baldwin Rd. This

stream was gauged on the south side of Baldwin road. This intermittent stream only had

33

flow in mid-June, with a discharge of 0.09 cubic feet per second. It was dried up

completely in July and August, however, in September through November, there was

water in the stream, but there was no flow registered by the stream gauge due to the

presence of leaves and other debris. Between June and November, the average

temperature was 17.4oC, and the average conductivity was 632 umhos.

Spiegleberg Creek (inflow 3) is located on Baldwin Rd. just south of Jake’s Rd.

and is the main stream flowing into Bear Lake. The stream was gauged on the west side

of Baldwin Rd. This stream reached its peak discharge at 2.1 cubic feet per second in

August. The average discharge between June and November was 0.74 cubic feet per

second, the average temperature was 17.1oC, and the average conductivity was 428.9

umhos.

The outflow of Bear Lake, a branch of the Lower Little Wolf River, was gauged

on the south side of Northshore Dr. Peak discharge occurred in late June and again in

early September, with a discharge of 3.6 and 3.3 cubic feet per second, respectively. The

average discharge measured at the outflow of Bear Lake between June and November

was 2.4 cubic feet per second; the conductivity ranged from 390 to 485 umhos, with an

average was 407 umhos. The average temperature from August to November was 16oC.

In January 2002, the outflow of Bear Lake was not completely frozen over near

Northshore Dr. The temperature of the outflow was 1.1oC and the conductivity was 396

umhos.

Mid-lake Water Quality Data

All mid-lake water quality data from the summer of 2001 are presented in

Appendix C. The following is a description of results for each major group of water

quality characteristics. Figure 3 displays where the mid lake samples were collected.

Dissolved Oxygen and Temperature

Bear Lake is typical of many northern temperate lakes in that its yearly cycle

includes two periods of stratification and two periods of water mixing. Stratification

occurs during both the winter and summer months. During the summer, the epilimnion,

or surface is 12-20 feet in Bear Lake and has a fairly constant temperature with dissolved

34

oxygen readings ranging from 9.3 mg/L in late May to 8.3 mg/L in late August. The

surface water temperature ranged from 16.3oC in May to 26.7oC in early August, and

back down to 13.6 oC in October. The average temperature of the epilimnion from May

through November was 19.8oC.

The epilimnion is followed by a strong temperature gradient, or thermocline, and

finally the Hypolimnion (Figure 15). Figure 16 displays one temperature profile per

month in Bear Lake, however, it should be noted that during the summer of 2001, profiles

were collected twice per month. All data is displayed in Appendix C. The water

temperature in the hypolimnion is warmer than the epilimnion in the winter months and

cooler in the summer months. The water temperature difference between the epilimnion

and hypolimnion creates a density difference between the two layers and in summer the

colder hypolimnion becomes isolated from mixing and addition of oxygen. Bacteria that

decompose plant residue and organic matter in the bottom sediments use up most of the

available dissolved oxygen in the hypolimnion. This results in low hypolimnion

dissolved oxygen concentrations, making this portion of the lake inhospitable to most life

forms.

Figure 15. Diagram of Lake Stratification

Epilimnion

Thermocline

Hypolimnion

35

Figure 16. Temperature profile in Bear Lake during summer stratification and fall turnover.

Monthly Temperature Profiles in Bear Lake

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30

Temperature (oC)

5/31/2001

6/27/2001

7/23/2001

8/22/2001

9/26/2001

10/8/2001

11/18/2001

1/17/2002

During the summer months of 2001, the hypolimnion had no measurable

dissolved oxygen. Warmer water temperature and an increase in biological activity can

create an anoxic hypolimnion during the summer months. The dissolved oxygen levels in

Bear Lake were below 1 mg/L at a depth of 14 feet in late July, and at a depth of 32 feet

in October. Bear Lake has a maximum depth of 62 feet deep, so during the summer

months of 2001, there was 44-50 feet of water with a low dissolved oxygen

concentration, in which aquatic life may be stressed to breathe. Figure 17 displays

monthly dissolved oxygen profiles in Bear Lake, however, it should be noted that profiles

were collected twice per month during the summer months of the 2001. All data are

displayed in the Appendix C.

Water mixing or turnover occurs in spring and fall, usually evident in April and

October or November. During fall turnover when the anoxic hypolimnion water began

to mix with the rest of the water column, dissolved oxygen concentrations at the bottom

of the lake increased from less than 1 in October, to 7.4 mg/L in mid-November. Lower

water temperatures, less biological activity, and the introduction of oxygenated water,

lead to an increase in dissolved oxygen in late fall.

36

Fall turnover and ice-free conditions lasted longer than normal in 2001 due to

unseasonably warm temperatures through December and January. Winter dissolved

oxygen levels ranged from 7.1 mg/L at the surface, to 2.9 mg/L at the lake bottom in

January. Temperature in January ranged from 1.5oC at the surface, to 3.5oC at the lake

bottom.

Dissolved oxygen data from the previous study shows that Bear Lake exhibited

anoxic conditions during the summer months at approximately the same depth as in 2001.

Figure 17. Monthly dissolved oxygen profile in Bear Lake during summer stratification and during fall turnover.

Monthly Dissolved Oxygen Profiles in Bear Lake

0

10

20

30

40

50

60

0 2 4 6 8 10 12

Dissolved Oxygen (mg/L)

5/31/20016/27/20017/23/20018/22/20019/26/200110/8/200111/18/20011/17/2002

37

Secchi Depth and Chlorophyll a Secchi depth is a measure of water clarity which includes small particulates and,

and it can often be directly compared to chlorophyll a, a measure of algae growth.

Chlorophyll a can also be an indicator of phosphorus levels (Shaw et. al. 1996). If

chlorophyll a is the source of suspended particles, higher chlorophyll a should correlate

to a shallower Secchi depth reading; however, many variables such as time of day and

wind can affect Secchi depth readings. Throughout the year, Secchi depth ranged from

6.8 to 16.3 feet with an average of 11 feet. Secchi depth reached its minimum from the

end of July through the end of August 2001. Chlorophyll a concentrations reached a

maximum in August and September (4.3 and 4.4 ug/L, respectively). Secchi readings did

inversely correlate somewhat with the chlorophyll a concentration; generally as

chlorophyll a concentrations decrease, Secchi depth increases (Figure 18). The data from

1982 displayed a strong correlation between the epilimnion TP concentration and

chlorophyll a concentration however, few data points existed to show much variability

throughout the growing season (Figure 19).

Based on relationships described in Shaw et al, 2000, Secchi depth in Bear Lake

ranked water clarity from fair to good (Table 2) in 2001. The Secchi data from 1980-82

ranked the water clarity in Bear Lake from poor to fair. Comparison of recent data with

data from about twenty years ago reveals that the chlorophyll a concentration has

decreased considerably while Secchi depth has increased.

38

Figure 18. Graphs show relationship between Secchi depth, chlorophyll a concentrations, and TP concentrations of the epilimnion of Bear Lake during the summer of 2001.

Secchi Depth vs. Chlorophyll a Concentration- Summer 2001

R2 = 0.3944

0

5

10

15

20

0 1 2 3 4 5

Chlorophyll a concentrations (mg/l)

2001 Chlorophyll a concentration vs. Epilimnion Total P concentration

R2 = 0.3778

0

5

10

15

20

25

0 0.01 0.02 0.03 0.04 0.05

Epilimnion Total Phosphorus concentration (mg/L)

Chl

orop

hyll

a co

ncen

trat

ion

(mg/

L)

39

Figure 19. Graphs show the relationship between epilimnion total phosphorus and chlorophyll a concentrations in Bear Lake, Waupaca Co., WI, from 1980-1982.

Bear Lake 1980-1982 EpilimnionTotal P concentration vs. Chlorophyll a concentration

R2 = 0.9945

05

10152025

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Total P concentration (mg/L)

Table 1. Water Clarity Index based on Secchi depth measurements

*Adapted from Shaw et al., 2000.

Water Clarity Secchi depth (ft)

Very Poor 3

Poor 5

Fair 7

Good 10

Very Good 20

Excellent 32

40

1980-82

2001

Conductivity, Alkalinity, Total Hardness, pH Conductivity, or what is sometimes called specific conductance is the measure of

the ability of a solution to conduct electrical flow. Conductivity increases with increasing

ion content, so the purer the water, the greater its resistance to electrical flow (Wetzel,

2001). Values are commonly two times the water hardness unless the water is receiving

high concentrations of contaminants introduced by humans (Shaw et al, 2000). The

average conductivity in Bear Lake in 2001 and 2002 was 393 umhos. Both the

epilimnion and hypolimnion average conductivity are approximately twice the water

hardness. Conductivity data was not collected in the 1975 and 1980-82 study.

According to Shaw et al., 2000, a lake’s hardness and alkalinity are affected by

the type of minerals in the soil and bedrock in the watershed, and by how much the lake

water comes into contact with these minerals. If a lake receives its groundwater from an

aquifer containing limestone minerals such as calcite (CaCO3) and dolomite (CaMgCO3),

hardness and alkalinity will be high, as is the case with Bear Lake. High levels of

hardness (greater than 150 mg/L) and alkalinity can cause marl (CaCO3) to precipitate

out of the water. This bi-product is harmless and can actually result in more fish

production and aquatic plants than soft water lakes (Shaw et al., 2000). It can also act as

a balancing mechanism, however, phosphorus precipitates with marl, thereby controlling

algae blooms.

The average alkalinity in 1975 was 176 mg/L, and from 1980-82 it was 195 mg/L.

The 2001-02 average alkalinity was 190mg/L. The average total hardness in 2001-02

was 206 mg/L. Total hardness data was not collected in the previous study. Bear Lake

has very hard water as shown in Table 2. Table 3 shows that Bear Lake is not very

sensitive to acid rain due to the carbonate buffering in the lake. Comparison of data from

1980-82 shows that the average alkalinity in Bear Lake has remained fairly constant over

the past twenty years.

41

Table 2. Categorization of Hardness by mg/L of Calcium Carbonate (CaCO3)

Level of Hardness Total Hardness as mg/L CaCO3

Soft 0 – 60 mg/L

Moderately Hard 61 – 120 mg/L

Hard 121 – 180 mg/L

Very Hard > 180 mg/L

*Adapted from Shaw et al., 2000.

Table 3. Sensitivity of Lakes to Acid Rain

Sensitivity to Acid Rain Alkalinity (mg/L CaCO3)

High 0 – 2 mg/L

Moderate 2 – 10 mg/L

Low 10 – 25 mg/L

Not Sensitive > 25 mg/L

*Adapted from Shaw et al., 2000.

An index of lake water’s acid level, pH is and important component of the

carbonate system. A pH of 7 is neutral and water with a pH of above 7 is considered to

be basic. This means that water with a higher pH will have less hydrogen ions than that

of acidic waters (lower pH). In Wisconsin, pH ranges from 4.5 in some acid bog lakes to

8.4 in hard water, marl lakes (Shaw et al., 2000). The average pH in Bear Lake in 2001

was 7.9, and since Bear Lake is a hard water, marl lake, it would be expected that the pH

would be around 8. The average pH of the epilimnion in the summer of 2001 was

slightly higher than 8.0, at a pH of 8.5, probably driven by plant growth. If the pH

increases above 9, it would force phosphorus to become soluble. The average pH of the

hypolimnion was slightly lower than 8.0, at a pH of 7.6. The January pH level was 8.1 in

the epilimnion and 8.2 in the hypolimnion. Due to the carbonate buffering in the lake,

the pH in Bear Lake has remained fairly constant over the past twenty-five years, at a

slightly basic pH of 8.

42

Total Phosphorus (TP) In more than 80% of Wisconsin’s lakes, phosphorus is the limiting nutrient

affecting the amount of weed and algae growth (Shaw et. al. 2000). Phosphorus enters

the lake through surface runoff, overland flow, groundwater inflow, and the inflowing

streams. The presence of wetlands where the inflowing streams converge may absorb

much of the phosphorus coming from within the watershed through these streams. In the

past, there were more barnyards and animals around the lake and within the watershed,

which contributed phosphorus to the lake. Local residents indicated that the algae

blooms were once more significant than they currently are. Also, agriculture practices

within the watershed have been focused on controlling sediment and nutrients, so it is

reasonable to believe that phosphorus in the lake will reduce over time if riparian inputs

are reduced as well.

In a marl lake such as Bear Lake, carbonate (marl/CaCO3) precipitates out of the

water as pH increases and carbon dioxide (CO2) is lost from plant uptake, increasing

water temperature and causing a decrease in carbon dioxide solubility and mixing.

Contact with the atmosphere allows the excess carbon dioxide to escape. Plants speed up

marl deposition by using carbon dioxide (CO2), which raises the pH and converts most

alkalinity to the carbonate. Phosphorus has been shown to co precipitate with carbonate

precipitation (marl) (Otsuki and Wetzel, 1972). Marl helps control algae growth in lakes,

by precipitating phosphorus, which is then unavailable for biological uptake.

Concentrations above 0.02 mg/L can initiate algae blooms.

According to Shaw et al., 2000, local sources of phosphorus are largely related to

human activities including soil erosion, non-Wisconsin purchased detergents, septic

systems, runoff from lawns or gardens, and agricultural fields or barnyards. Dishwasher

detergents contain phosphorus, whereas laundry detergents purchase in Wisconsin do not.

Regional sources may include animal wastes along with runoff from farmlands.

Dissolved reactive phosphorus is the form of phosphorus that is available for plant

and algae uptake, however, total phosphorus (TP) was used in these comparisons rather

than reactive phosphorus because its levels remain more constant and are not affected by

rapid cycling due to aquatic organisms (Shaw et al., 2000).

43

The average epilimnion TP concentration in 2001-02 ranged from 0.013 to 0.045

mg/L with an average of 0.027 mg/L. This average concentration is great enough to spur

algae blooms and aquatic plant growth. Since the TP concentrations fluctuate throughout

the growing season, and the previous study took quarterly samples, the data was

compared by month (Figure 20). The TP concentration in 1975 ranged from 0.028 to

0.050 mg/L with an average of 0.040 mg/L. The 1980-82 epilimnion TP concentration

ranged from 0.02 to 0.06 mg/L, with an average of 0.04 mg/L. TP concentrations in the

epilimnion of Bear Lake fluctuate throughout the 2001 study, but overall have slightly

decreased over time. As variation of TP concentrations can occur on an annual basis,

with rainfall or climatic variation, efforts should be made to collect samples for TP

analysis on an ongoing basis.

The hypolimnion TP concentration in 1980-1982 ranged from 0.04 to 0.16 mg/L

with an average of 0.08 mg/L, whereas, the hypolimnion TP concentration in 2001-02

ranged from 0.023 to 0.154 mg/L with an average of 0.072 mg/L. This shows that the

concentration of TP in the hypolimnion also fluctuates throughout the year and has

remained fairly constant over the past twenty years. Higher levels of phosphorus in the

hypolimnion during the summer months can be attributed to anoxic conditions causing a

release of phosphorus from the bottom sediments. Due to stratification, the hypolimnion

does not mix with epilimnion water until turnover. When the water does mix,

phosphorus levels in the epilimnion can increase (Voss et al., 1992), as observed in the

November sample at Bear Lake. The increased phosphorus concentration in the

epilimnion can lead to fall algal blooms, which occurred in the fall and early winter in

Bear Lake during 2001. Once these nutrients are in the lake, they are very difficult to

remove because they get recycled. Bear Lake can loose some of its phosphorus load to

the stream flowing out of the lake, which flows into the Lower Little Wolf River.

44

Figure 20. Graph of the epilimnion and hypolimnion total phosphorus concentrations in Bear Lake, Waupaca Co., WI, by month for each sample year.

Epilimnion Total Phosphorus by month

0

0.02

0.04

0.06

0.08

J F M A M J J A S O N D

Sample date

197519801981198220002001

Hypolimnion Total Phosphorus by month

0

0.05

0.1

0.15

0.2

J F M A M J J A S O N D

Sample date

1980

1981

1982

2001

Nitrogen

Nitrate-N and ammonium-N are two forms of nitrogen that are readily available to

plants and can rapidly move to groundwater and surface water. Nitrogen is second only

to phosphorus as an important nutrient for plant and algae growth (Shaw et al., 2000). It

also represents a threat to human health, especially in the form of nitrate because of its

association with methemoglobinemia (Blue Baby Syndrome) in infants (VanRyswyk,

45

1996). In Wisconsin, nitrogen does not occur naturally in most soil minerals, but is a

major component of organic matter (Shaw et al., 2000). According to Shaw et al. (2000),

nitrogen compounds often exceed 0.5 mg/L in rainfall, so that precipitation may be the

primary nitrogen source for pristine seepage and some drainage lakes. The amount of

nitrogen in lake water usually is strongly related to local land use such as septic systems

or lawn and garden fertilizer used on lakeshore property. Nitrogen may also come from

sources within the watershed that include fertilizer and animal wastes on agricultural

lands. This nitrogen can then enter the lake through surface runoff or groundwater

inflow.

The forms of nitrogen that were analyzed include NH4+ (ammonium), NO2

- +

NO3- (nitrite + nitrate), and Total Kjeldahl Nitrogen (TKN), which is organic nitrogen

plus ammonium. TKN tends to occur in higher levels in hard water lakes as a result of

relatively high inputs in calcareous regions and low amounts of biological uptake because

of low productivity (Wetzel, 1983). TKN includes both inorganic forms of nitrogen

(NO3+NO2 and NH4+) and organic N. Both forms of inorganic nitrogen (NO3+NO2 and

NH4+) are used by aquatic plants and algae and are very soluble, which means they are

readily leached to groundwater. These forms can be transformed to organic N, and from

organic N back to the inorganic forms through the nitrogen cycle (Figure 21)(Shaw et al.,

2000).

The epilimnion concentration of ammonium in 1975 ranged from 0.05 to 0.51

with an average of 0.23 mg/L and in 1980-82, it ranged from 0.02 to 0.81 mg/L with an

average of 0.47 mg/L. The epilimnion ammonium concentration in 2001-02 ranged from

0.01 to 0.58 mg/L. The ammonium concentration in the hypolimnion in 2001-02 range

from 0.41 to 1.4 mg/L with an average of 0.476 mg/L. Figure 22 shows ammonium

concentrations in Bear Lake by month. Elevated levels of all analyzed forms of nitrogen

were found in the anoxic hypolimnion throughout the summer and in early October. The

ammonium concentrations fluctuate throughout the growing season and have remained

relatively constant since 1975.

The greatest concentrations of NO2 + NO3 in 2001 were found within the

thermocline or middle layer of the lake, at 1.29 mg/L in late April. This is likely due to

sediment release of nitrogen during turnover. The epilimnion concentration of NO2 +

46

NO3 in 2001-02 ranged from 0.02 to 1.29 mg/L with an average of 0.22 mg/L. The

concentration of NO2 + NO3 in 1975 ranged from 0.01 to 0.51 mg/L, and in 1980-82 the

epilimnion concentration ranged from 0.02 to 1.1 mg/L. The epilimnion or surface

concentration of NO2 + NO3 has remained fairly constant since the late 70’s and early

80’s and is relatively low.

Figure 21. Schematic showing various forms of nitrogen and its movement in the environment. (University of Minnesota. 2002)

The NO2 + NO3 concentrations in the hypolimnion in 2001-02 ranged from 0.002

to 1.290 mg/L with an average of 0.206 mg/L. The NO2 + NO3 concentration in the

hypolimnion in 1980-82 ranged from 0.02 to 0.37 mg/L with an average of 0.08 mg/L.

Figure 23 shows the NO2 + NO3 concentrations by month in order to compare the data

from the previous study. The NO2 + NO3 concentrations fluctuate throughout the

growing season and with precipitation, however, it should be noted that the greatest

concentrations are available during spring overturn which likely stimulates early algae

and macrophyte growth.

47

Figure 22. Epilimnion and hypolimnion ammonium concentrations in Bear Lake by month.

Epilimnion Ammonium concentraions in Bear Lake by month

0

0.2

0.4

0.6

0.8

1

J F M A M J J A S O N D

Sample date

1975

1980

1981

1982

2001

Hypolimnion Ammonium concentrations in Bear Lake by month

00.20.40.60.8

11.21.41.6

J F M A M J J A S O N D

Sample date

1980

1981

2001

48

Figure 23. NO2 + NO3 concentrations by month in Bear Lake, Waupaca Co., WI.

Epilimnion or surface NO2+NO3 concentrations by month

00.20.40.60.8

11.21.4

J F M A M J J A S O N D

Sample Date

197519801981198220012002

Hypolimnion NO2+NO3 concentrations by month

00.20.40.60.8

11.21.4

J F M A M J J A S O N D

Sample date

1980

1981

2001

Figure 24 shows the concentration of Total Nitrogen in the epilimnion fluctuates

within the growing season and with rainfall. Total Nitrogen was calculated by adding the

NO2+NO3 concentration to the TKN concentration.

49

Figure 24. Total Nitrogen concentrations by month in Bear Lake, Waupaca Co., WI.

Epilimnion Total Nitrogen Concentrations by month

0

0.5

1

1.5

2

2.5

J F M A M J J A S O N D

Sample date

198119822001

Hypolimnion Total Nitrogen by month

0

0.5

1

1.5

2

2.5

J F M A M J J A S O N D

Sample date

1981 Total N2001 Total N

The epilimnion TKN concentration in 2001-02 ranged from 0.75 to 1.18 mg/L

with an average of 0.89 mg/L. The epilimnion TKN concentrations in 1980-82 ranged

from 0.08 to 1.1 mg/L with an average of 0.876 mg/L. This shows that the epilimnion

TKN concentrations have remained fairly constant (Figure 25).

50

The hypolimnion TKN concentrations in 1980-82 ranged from 1.5 to 2.3 mg/L

with an average of 1.65 mg/L. The 2001-02 hypolimnion concentrations ranged from

0.76 to 2.34 mg/L with an average of 1.32 mg/L. Nitrogen levels in the hypolimnion

have remained fairly constant over the past twenty to twenty-five years.

Figure 25. Epilimnion TKN concentrations by month in Bear Lake, Waupaca Co., WI.

Epilimnion TKN concentration by month

0

0.2

0.4

0.6

0.8

1

1.2

1.4

J F M A M J J A S O N D

Sample date

1981

1982

2001

Hypolimnion TKN concentrations by month

0

0.5

1

1.5

2

2.5

J F M A M J J A S O N D

Sample date

198120012002

51

During fall turnover, the concentrations of all analyzed forms of nitrogen were

greater than the average epilimnion concentrations from May through October 2001. The

average concentrations of these forms of nitrogen in the hypolimnion during the same

time period were greater than the concentrations in the fall turnover sample, showing that

the higher concentrations of hypolimnion nitrogen was mixed with the lower

concentrations of the epilimnion resulting in an overall concentration somewhere in

between the epilimnion and hypolimnion averages after fall turnover.

Sediment, Macrophyte, and Interstitial Water Study

Interstitial water is the pore water in the upper 6-12” of sediment. This water can

be nutrient rich and undergoes a significant amount of biological activity. It is the water

in contact with the roots of aquatic macrophytes. Interstitial water also serves as a source

of nitrogen and other essential nutrients (Wetzel, 1983). Absorption of nutrients from the

water column does occur, but it is dependent on the concentration of the nutrient in the

water. Algae more readily accomplishes nutrient uptake from the water column. When

algae die and decompose in bottom sediments, nitrogen, phosphorus and other nutrients

become available in the interstitial water due to the anaerobic, reducing environment

provided by the sediment. These elements are less soluble in aerobic sediments or in

aerobic lake water (Hudson, M., Shaw, B.H., and Reas, L., 1998-99).

While it has been fairly well accepted that submerged aquatic plants receive the

bulk of their nutrient supply from sediment pore water, it is poorly understood what

factors are responsible for aquatic plant growth and distribution (Welch, 1992). Certainly

sediment type, organic matter content, groundwater inflow or outflow areas, slope, and

nutrient and light availability will all contribute to the suitability of a site for colonization

by a certain species or many species of aquatic plants.

In attempt to draw relationships between interstitial water, plant growth, and

sediments, a study was conducted to determine whether the data correlated to the

distribution and biomass of aquatic plants. However, since there were only 12 sites

sampled, attempts to draw significant correlations become difficult due to different

physical, chemical, and human impacts at each site. Therefore each site or group of sites

52

with similar characteristics will be discussed separately. The interstitial water, plant, and

sediments sites are displayed in Figure 6 and the data are displayed in Appendix D.

Interstitial sites 2, 4 and 6 are located on the East side of the lake, north of the

boat landing. Site 2 is in an area that has moderate shoreline development and a sandy

bottom with little or no aquatic vegetation. Site 2 had elevated levels of ammonium and

chloride in the interstitial water and elevated levels of potassium (K) and sulfate (SO4) in

the sediments. Site 4 was located just south of the Bear Lake campground beach near a

wetland area. This site had a sandy bottom and did not have any elevated nutrient

concentrations or aquatic plants. Site 6 had elevated levels of ammonium in the

interstitial water and did not have many aquatic plants.

Site 8 had elevated levels of reactive phosphorus and ammonium in the

interstitial water, however, had the lowest concentrations of TKN, TP and percent

biomass in the plant tissues collected. The sediments at this site contained the greatest

total percent solids of all the sample sites on the lake.

Site 10 is located near the east side of the lake in an area with shoreline

development most of which is not used full time year round. The interstitial water data

shows that this site had the greatest concentration of nitrate and nitrite at 0.04 mg/L. The

plant tissues at this site had slightly elevated TKN and TP concentrations. The sediments

at this site contained high levels of nutrients, but had a low percent organic matter.

Site 12 is located in a wetland area, on the north end of the lake. This site had the

highest concentrations of all analyzed nutrients in the sediments. These concentrations

were at least double the concentration of any other site on the lake, in all of the nutrients

in the sediments. This site may still be seeing impacts from an old barnyard up the hill

from this wetland area, which is no longer in agricultural use. Chara and pond lily were

the dominant plant species at this site. The plant tissues from this site had the second

highest concentrations of TKN and TP. However, the interstitial water had no elevated

levels of nutrients.

Site 14 is located on the northwest end of the lake and has moderate shoreline

development. Site 14 had the greatest concentration of reactive P in the interstitial water

on the lake, however there was no aquatic plant growth. The sediments at this site had

the lowest nutrient concentrations in the lake, and contained the most percent organic

53

matter. This site also had the lowest total percent solids in the sediments. At this site, the

samples were collected from the boat due to lack of solid ground to stand on. Aquatic

plant growth at this site may have been hindered due to disturbance by human activity.

Sites 16 through 22 are located on the west side of Bear Lake which does not have

any shoreline development; this may explain some differences between the east and west

sides of the lake. Thick aquatic vegetation predominantly chara and pond lily line the

west side of the lake, which also has a thick buffer of natural woody and wetland

vegetation, which provides critical fish and wildlife habitat.

Sites 24, 16 and 18 had the highest percent biomass possibly due to the fact that

these areas have not been developed and do not receive as much disturbance as areas on

the east side of the lake. The greatest concentration of ammonium in the interstitial water

was found at site 16. This may be due to the high concentrations of ammonium flowing

into the lake via shallow groundwater near this site, which was determined by the mini-

piezometer study. Site 18 had elevated levels of reactive phosphorus and chlorides in the

interstitial water. Analysis of the sediment reveals that elevated levels of NO2+NO3

were found at sites 16 and 18. Site 20 had no elevated levels of nutrients in the

sediments or interstitial water, and no aquatic plants were located at this site. Site 22 had

the greatest concentration of chloride in the lake, but did not have elevated levels of

nutrients in the interstitial water. The aquatic plant tissues collected at this site had

elevated levels of TKN and TP. Chara was the predominant plant species present at this

site.

Site 24 is located on the southwest end of the lake by a large wetland area. This

wetland area is made up of three converging streams, which flow into Bear Lake. These

streams carry nutrients and sediments from within the watershed, however, the wetland

area may be retaining some of these nutrients from entering the lake. Site 24 had

elevated ammonium concentrations in the interstitial water and had the greatest

concentration of TKN in the plant tissues. This site also had the highest percent biomass

on the lake, possibly due to lack of human disturbance.

Analysis of plant tissues from each site revealed that the greatest concentrations

of TKN in plants were at sites 24, 12 and 22, which are located in wetland areas with

thick aquatic vegetation. The greatest concentrations of TP in the plant tissues were

54

found at sites 22, 12, 10 and 24, respectively. The interstitial water reactive phosphorus

concentration had a moderate correlation with the percent biomass in the plant tissues

collected (Figure 26). Generally, as the interstitial water reactive phosphorus

concentration decreases, the percent biomass in the plant tissues increases. Percent

biomass also had a fairly strong correlation with nutrient levels in the sediment, with the

exception of site 12. Generally, as TKN and TP concentrations in the plant tissue

increases, reactive P, ammonium and nitrate levels of the interstitial water decrease,

showing that the plants are using the available nutrients in the interstitial water.

Site 12 had the highest levels of all of the nutrients analyzed in the sediments,

however, did not have the greatest percent biomass. The high nutrient concentrations in

the sediments at this site are likely due to impacts from an old abandoned barnyard that

was located up the hill from this area. The dominant plant species at site 12 was chara

and pond lily.

Noticeably elevated concentrations of chloride were found at sites 22, 2, and 18

with concentrations of 26.6, 23.0 and 22.0 mg/L respectively. The average concentration

of chloride in the interstitial water was 14.5 mg/L. Site 2 is located on the southeast side

of the lake where there is heavy shoreline development and the area has been influenced

by local impacts. Sites 18 and 22 have no shoreline development and are in undisturbed

areas with an abundance of aquatic vegetation.

Figure 26. Shows that as the interstitial water reactive P concentration increases, the percent biomass in the plant tissues increases.

Percent Biomass vs. Interstitial water Reactive Phosphorus

R2 = 0.3638

0

5

10

15

20

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Interstitial water Reactive Phosphorus concentration (mg/L)

55

Groundwater Study

Mini-piezometers were inserted approximately every 200-300 feet in the lake

bottom, and used to collect shallow groundwater samples for chemical analysis along

with general information regarding groundwater inflow or outflow around the lake. A

map of mini-piezometer sites can be found in Figure 4, and all mini-piezometer data can

be found in Appendix E. Hydraulic head data were collected at sixty-nine sites around

the lake using mini-piezometers and the Hvorslev slug test (Hvorslev, 1951) in August of

2001. This information was used to estimate water and nutrient budgets for the lake.

Samples were collected at all up-welling or ground water inflow sites, along with

a couple samples from no-welling sites, where the groundwater is not flowing in or out of

the lake. Down-welling or groundwater outflow sites will have concentrations similar to

lake water, since the lake water is feeding the groundwater. The regional groundwater

flow is from the southwest to the northeast end of the lake. The shallow groundwater

inflow and outflow around Bear Lake determined by this study was sporadic. Figure 27

shows the shallow groundwater flow direction around Bear Lake. Approximately 44%

(30 sites) of the sites were up-welling sites, 55% (38 sites) were no-welling sites and only

1% (1 site) on the northeast end of the lake was a down-welling site. The greatest

velocity of groundwater is entering the lake at sites 47 and 45.

Temperature and conductivity were measured in the field and the samples were

transported on ice to the Environmental Task Force Lab and analyzed for NO2 + NO3,

chloride, ammonium, and reactive phosphorus. This information provides a general

overview of the relationship between local land uses and shallow groundwater quality.

As samples were taken every 200-300 feet, this information should not be used to

determine fertilizer and septic inputs on a specific property. Data will be interpreted

using site impact classifications which include locally impacted, wetland impacted,

wetland/locally impacted and non-impacted.

The presence of chloride, where it does not occur naturally indicates possible

water pollution (Shaw et al., 2000). In fact, septic systems do not effectively remove

chloride due to its anionic form and conservative or non-reactive nature and as a result

are often an indication of contamination from man-made sources. Chloride is a common

constituent in animal and human wastes, potash fertilizer (potassium chloride), and often

56

Figure 27. Shallow groundwater inflow/outflow determined by mini-piezometers around Bear Lake.

57

a component of road deicing agents. Chloride concentrations above 2 mg/L indicate an

impact on water quality. Over 80% of the sites had chloride concentrations greater than 2

mg/L. One-third of the mini-piezometer sites had chloride concentrations greater than 10

mg/L. Figure 28 shows the mini-piezometer chloride concentrations around Bear Lake.

Locally impacted sites may include impacts from septic systems, road salts,

abandoned barnyards or lawn and garden fertilizers. Septic, abandoned barnyard, and

lawn and garden fertilizer influenced sites will usually have elevated chloride and nitrate

values, while having isolated amounts of reactive phosphorus or ammonium. Sites

affected by road salts will strictly have elevated chlorides. Sites grouped under locally

impacted sites, may include a combination of these factors. Approximately 37% of the

sampled mini-piezometer sites fall into this category. Chloride concentrations at locally

impacted sites range from 3.0 to 81.0 mg/L with an average of 19.0 mg/L. NO2+NO3

concentrations at locally impacted sites range from 0.02 to 5.8 mg/L with an average of

0.70 mg/L. Sites 42-47 are located in an area that is close to Highway 22-110 and appear

to be influenced by several local impacts. Sites 57-59 also appear to be influenced by

local impacts.

Wetland impacted sites were identified by elevated levels of reactive phosphorus

and ammonium. Concentrations of nitrate and chloride were minor or non-existent.

Sources of ammonium and reactive phosphorus from wetlands are from decomposition

and release of nutrients from organic matter. Figure 29 shows the mini-piezometer

ammonium concentrations around Bear Lake. Approximately 12% of the mini-

piezometer sites appeared to be wetland impacted sites. Sites 4, 5, 33, and 36 were

identified as wetland impacted sites. Concentrations of reactive phosphorus ranged from

0.003 to 0.095 mg/L with an average of 0.031 mg/L. Figure 30 shows reactive

phosphorus concentrations around Bear Lake.

Ammonium concentrations at wetland impacted sites ranged from 0.34 to 1.90

mg/L with an average of 1.01 mg/L. Chloride concentrations at wetland impacted sites

ranged from 0.5 mg/L to 5.0 mg/L with an average of 1.9 mg/L.

58

Wetland/locally impacted sites demonstrate at least some concentration of all the

examined nutrients along with detectable chloride levels. There is likely a combination

of sources for these sites, as indicated by the complex water chemistry. Abandoned

barnyards around Bear Lake may also be contributing nutrients to the lake via

groundwater. Nearly 40% of the sampled mini-piezometer sites appeared to be

wetland/locally impacted. Chloride concentrations at wetland/locally impacted sites

ranged from 1.0 to 39.0 mg/L with an average of 8.3 mg/L. Reactive phosphorus

concentrations ranged from 0.003 to 1.900 mg/L with an average of 0.530 mg/L.

Areas of high nutrient groundwater inflow possibly from septic systems, is

contributing to the excessive aquatic plant growth found in many parts of the lake. An

elevated concentration of chloride is an excellent indicator of septic or fertilizer

contamination when accompanied by elevated reactive phosphorus, and ammonium or

nitrate. Approximately 20% of the mini-piezometer sites appear to be impacted by septic

systems. Sites 1, 32, 35, 45, 47, and 67 had elevated concentrations of NO2+NO3 and

chloride in the shallow groundwater flowing into Bear Lake. Sites 67, 45, and 47 had the

three greatest concentrations of NO2+NO3 at concentrations of 20.50, 5.80 and 2.89

mg/L, respectively, and three of the four greatest chloride concentrations. Figure 31

shows mini-piezometer NO2+NO3 concentrations around Bear Lake. The groundwater at

sites 47 and 45 is flowing into Bear Lake with the greatest velocity of any of the sites

sampled on the lake. Therefore, these sites are contributing nutrients to the lake at a

greater rate than anywhere else on the lake.

Non-impacted sites are sites that demonstrated little or no concentrations of all

aspects measured. The chemistry at these sites will best represent unaffected shallow

groundwater flow to Bear Lake. Sites 14, 51, 52, 62, and 64 were classified as non-

impacted sites. Non-impacted sites comprised about 14% (5 sites) of the sampled mini-

piezometer sites. Chloride concentrations at non-impacted sites range from 1.5 to 10.0

mg/L with an average of 5.3 mg/L. Concentrations of all other nutrients were low at

these sites.

Sites 6-13, with the exception of site 11, are located on the southwest edge of the

lake, and yielded no water due to the fine marl sediments sealing up the holes in the mini-

piezometer screen. The water that was pulled up through the mini-piezometer in this area

59

and at site 25 was of a white milky consistency due to the marl sediments, however,

enough water could not be drawn through the mini-piezometer in order to make sure that

a representative groundwater sample could be taken. Since the shallow groundwater flow

associated with these sites has little to no contact with the lake water, these sites were

classified as no-welling sites.

60

Figure 28. Map of mini-piezometer chloride concentrations around Bear Lake.

61

Figure 29. Mini-piezometer ammonium concentrations around Bear Lake.

62

Figure 30. Map of mini-piezometer reactive phosphorus concentrations around Bear Lake.

63

Figure 31. Map of mini-piezometer NO2+NO3 concentrations around Bear Lake.

64

Trophic Status Index

The trophic status is another way to characterize water quality. Lakes are

classified into one of three stages based on trophic state – oligotrophic, mesotrophic, and

eutrophic (Shaw et al., 2000). The status reflects a lake’s nutrient and clarity levels.

These categories are related to the natural aging of a lake, however, this aging process

can be accelerated by changing the riparian zone and land uses within a lake’s watershed.

According to Shaw et al., oligotrophic lakes are generally clear, deep and free of

weeds or large algae blooms. They are low in nutrients and do not support large fish

populations, but can support a fishery of large game fish. Oligotrophic lakes are often

limited by phosphorus and contain nitrogen in quantities in excess of demand from

growth supported by available phosphorus (Wetzel, 2001). Oligotrophic lakes are

“young” lakes. As the lake becomes more productive, the primary effecting agent is

increased loading of phosphorus.

Eutrophic lakes are high in nutrients and support a large biomass (all plants and

animals living in the lake). They are usually either weedy or subject to frequent algae

blooms, or both. Eutrophic lakes often support large fish populations, but are also

susceptible to oxygen depletion. Small, shallow, eutrophic lakes are especially

vulnerable to winter kill which can reduce the number and variety of fish.

Mesotrophic lakes lie between the oligotrophic and eutrophic stages. They are

void of oxygen in late summer, and the hypolimnion limits cold-water fish and cause

phosphorus cycling from sediments.

Common measures of trophic status include Secchi depth (water clarity), total

phosphorus (TP) concentration, and chlorophyll a concentration (measure of algae).

Although many factors influence these relationships, the major assumptions that bring the

Trophic State Indices (TSI) together are that 1) the amount of chlorophyll a present is

primarily related to the phosphorus concentration, and 2) water clarity is primarily

dependent on the chlorophyll a concentration (Lillie, 1983). Usually, as total phosphorus

values increase, the chlorophyll a levels also elevates while the Secchi depth decreases

due to algal communities in the lake profile.

There have been several Trophic State Indices developed in an attempt to translate

several of the measurable water chemistry variables into an assessment of lake water

65

quality. The indices are valuable in comparing both water quality changes over time in a

given lake, as well as quantitative comparisons to other lakes. The most representative

set of equations was taken from Lillie and Graham (1993), which are based on the Bureau

of Research’s 1979 random survey data set (combined lakes and impoundments) that

were greater than 5 feet deep and at least 25 acres in size. It uses existing Wisconsin

databases to derive area specific formulas. The calculations were based on monthly

sampling periods during the summer months defined as May through September.

Average summer secchi depth and chlorophyll a values were calculated using data from

the summer of 2001. The average summer TP was calculated using a weighted TP value.

The equations used to determine WTSI values are listed below:

WTSI (SD)= 60-14.4 ln(SD)

where SD is the average summer (May-September) secchi depth in meters.

WTSI (CHL)= 34.8+(7.56 ln(CHL))

where CHL is the average summer (May-September) chlorophyll a concentration in

(ug/L).

WTSI (TP)= 28.2+(7.73 ln(TP))

where (TP) is the average weighted summer (May-September) Total phosphorus concentration in (ug/L).

The weighted TP value was determined by weighting each layer concentration

proportionally to its volume of the water column. In order to compare the data from the

1980-82 study, the TP concentrations were also weighted proportionally to its volume in

the water column.

Since there is no chlorophyll a data from 1975, the trophic state index could not

be applied to that data. Since the data from 1980-82 contains secchi depth, chlorophyll a

and TP concentrations may be applied to the trophic state index, however, there was only

one sample taken in each summer, and quarterly samples were collected, so all the

samples dates were averaged to determine a 1980-82 average. Table 4 presents the

summer averages and the WTSI data from 1980-82 and 2001.

66

Table 4. 1980-82 and 2001 average summer Secchi depth, chlorophyll a concentrations, weighted TP values with calculated WTSI equivalent values.

Secchi Depth (feet)

Secchi Depth

(meters) WTSI(SD) Chlorophyll a

(ug/L) WTSI(CHL)

TP concentration

(ug/L) WTSI(TP) 1980-82 5 1.5 54.2 11 52.9 70* 61.0 2001-02 10.5 3.4 42.5 3.7 44.7 75.1* 59.4 *Total Phosphorus values were calculated using layer concentrations weighted by volume

of the water column.

In general, the lower the WTSI equivalent value, the better the water quality is.

Using the Lillie and Mason Water Quality Index (Table 5), the 1980-82 data rate Bear

Lake’s apparent water quality as fair to poor. Using the Lillie and Mason Trophic

Classification (Table 6), the 1980-82 data classified Bear Lake as a eutrophic lake.

Chlorophyll a content was measured monthly from May through September 2001,

and ranged from 1.1 to 4.4 ug/L, with an average of 2.98 ug/L. Secchi depth ranged from

2.0 to 5.0 meters in the summer of 2001, with an average of 3.4 meters. Using the Lillie

and Mason Water Quality Index (Table 5), Bear Lake has very good water quality when

examining Secchi depth, and chlorophyll a content. However, TP levels rank the lake’s

apparent water quality as poor. Using the Lillie and Mason Trophic Classification

(Table 6), the average summer chlorophyll a concentration and Secchi depth, Bear Lake

presented characteristics of an oligotrophic lake. This shows a decrease in chlorophyll a

and TP concentrations and an increase in Secchi depth over the past twenty years.

TP values may be elevated in the lake because of a chemical reaction that

produces marl. TP is a measure of all the phosphorus in the sample and is not the

phosphorus available for plant uptake. If the amount of carbonate (CO3) is high enough,

it will react with calcium in the water to form CaCO3 (marl). Marl precipitates out

leaving a white substance in the sediment and can often be observed as white residue on

plant leaves. The marl precipitate bonds with phosphorus, thereby eliminating its

availability to the plant community and reducing algae growth.

Also, the plant community can only take up phosphorus that is not rendered

unavailable to plants through marl precipitation. TP values may actually be much higher

67

in Bear Lake due to macrophyte growth, since plants contain and utilize phosphorus for

growth.

Improvements of all parameters of the trophic status index present an

improvement in apparent water quality and a slight improvement in the trophic state since

the late 1970’s and early 1980’s. Overall, the TSI determines Bear Lake’s current water

quality conditions as mesotrophic to eutrophic. Bear Lake does exhibit characteristics of

a eutrophic lake such as: oxygen depletion, algal blooms, abundance of aquatic

macrophytes and elevated nutrient concentrations, while exhibiting characteristics of an

oligotrophic lake such as good water clarity. With the carbonate buffering in the lake,

and reduction of inputs of phosphorus via groundwater and surface runoff, Bear Lake

may continue to see improved water clarity.

Table 5. Apparent water quality categories for Wisconsin lakes based on chlorophyll a content, water clarity, and Total P concentrations.*

Water Quality Index

Approximate Chlorophyll a

Equivalent (ug/L)

Approximate Secchi Depth Equivalent (m)

Approximate Total P

Equivalent (ug/L)

Approximate TSI**

Equivalent Excellent <1 >6.0 <1 <34 Very Good 1 to 5 3.0-6.0 1 to10 34-44 Good 5 to 10 2.0-3.0 10 to 30 44-50 Fair 10 to 15 1.5-2.0 30 to 50 50-54 Poor 15 to 30 1.0-1.5 50 to 150 54-60 Very Poor >30 <1.0 >150 >60 *From Lillie and Mason (1983) **From Carlson (1977)

68

Table 6. Trophic classification of Wisconsin lakes based on chlorophyll a, water clarity measurements, and total phosphorus values. (Adapted from Lillie and Mason, 1983.)

Trophic class

Total Phosphorus

(ug/L) Chlorophyll a

(ug/L) Secchi disc

feet Oligotrophic 3 2 12

10 5 8 Mesotrophic 18 8 6

27 10 6 Eutrophic 30 11 5

50 15 4

Bear Lake-2001 56.3 2.98 11.1 *Adapted from Shaw et al., 1996.

Aquatic Macrophyte Survey (contributed by Stacey Allen)

Aquatic macrophytes (larger sized plants) have apparently been abundant in Bear Lake for some time. A 1954 survey indicated that aquatic macrophytes approached nuicance levels in some parts of the lake. Pondweeds were most common, with big leaf pondweed predominating. No water milfoil was observed at that time. In 1959, big leaf pondweed was again the most widely distributed species and an influx of water milfoil was documented. In some eutrophic lakes water milfoil becomes quite abundant by out-competing other aquatic plants. In October 1973, big leaf pondweed was described as excessive in certain areas of the lake and American lotus (Nelumbo lutea) was documented. American lotus is becoming rare and is a protected species in Wisconsin. A survey in the summer of 1975 again indicated that aquatic vegetation, particularly pondweeds was abundant in Bear Lake. Water milfoil was now described as excessive. Some musk grass, wild celery, and bushy pondweed were also noted (Bushweiler, B. and Rasman, T. 1984.). The survey of aquatic vegetation conducted during the summers of 1980-81

revealed that Lemna spp., Nymphaea spp., Nuphar spp., Ceratophyllum demersum,

Myriophyllum exalbescens, Chara spp., and Potamogeton praelongus were abundant

aquatic plants in Bear Lake. The 2001 aquatic plant survey did not identify

Myriophyllum exalbescens and Potamogeton praelongus within Bear Lake.

69

The survey of aquatic vegetation conducted during the summers of 1980-81

revealed that Heteranthera dubia, and Potamogeton natans, were aquatic plants common

in Bear Lake, however, they were not identified in the 2001 aquatic plant survey. Since

there were only 25 transects, it is possible that this survey did not locate these species, or

they could have been eliminated from the lake ecosystem.

The latest survey of aquatic vegetation was conducted during the summer of 2001.

The three species with the greatest total occurrence in Bear Lake were Chara sp., Najas

flexilis and Potomageton zosteriformis. The two species with the least total occurrence

were Myriophyllum spicatum and Spirodela polyrhiza. In depth zones one, two, and

three Chara sp. had the highest total occurrence. In depth zone four, Ceratophyllum

demersum had the highest total occurrence.

The 2001 aquatic plant survey revealed the presence of the exotic species of

Eurasian milfoil on the north end of the lake. Eurasian water milfoil (Myriophyllum

spicatum) is a submersed aquatic plant native to Europe, Asia and northern Africa. It is

one of eight milfoil species found in Wisconsin and the only one non-native to the state.

Generally, the plant goes unnoticed until it has established itself in a lake and become a

nuisance. Eurasian water milfoil first showed up in Wisconsin's counties in the 1960's.

In the past three decades, this exotic species has significantly expanded its range,

especially over the last five years from 1994 to 2001. Boats or boat trailers that have

aquatic plants from another body of water usually transport Eurasian milfoil. Since the

boat landing is on the south end of the lake, boats that were not launched from the boat

landing may have introduced this exotic species into Bear Lake. Since the exotic species

is only found in a small area of the lake, the spread of this species should try to be

controlled.

Because of its potential for explosive growth and its incredible ability to

regenerate, Eurasian water milfoil can successfully out compete most native aquatic

plants, especially in disturbed areas. In a number of Wisconsin lakes, Eurasian water

milfoil has formed huge monoculture stands with vast mats of surface foliage that shade-

out native aquatic plants and diminish the aesthetic beauty. Recreational activities like

swimming, boating and sport fishing are also diminished on lakes infested with Eurasian

water milfoil. A variety of techniques have emerged for controlling Eurasian water

70

milfoil populations on Wisconsin's lakes. These techniques include mechanical cutting

and harvesting in open areas, limited use of herbicide treatments and more recently the

introduction of weevils as a biological control agent.

2001 Bear Lake Aquatic Plant Survey Methodology

Sampling methods were based on the rake-sampling method developed by Jessen

and Lound (1962) and currently used by the Wisconsin DNR. Site location was

accomplished by measuring the shoreline of Bear lake using a cartometer and then

dividing the shoreline into 25 equal segments. A transect, perpendicular to the shoreline,

was randomly placed within each segment.

Sampling sites were randomly located within depth zones of 0-2 ft., 2-5 ft., 5-10 ft

and 10-20 ft along each transect. Locations of each site were recorded on a map. Four

rake samples were taken at each sampling site using a long-handled, steel-thatching rake.

The four samples were collected from each quarter of a 6-foot diameter quadrant.

Aquatic plant species collected on each rake sample were hand identified and each

species were given a density rating (0-5) based on the number of rake samples on which

it was present at each sampling site. A rating of 1 indicates that a species was present on

one rake sample, a rating of 4 indicates that it was present on all four rake samples and a

rating of 5 indicates that it was abundantly present on all rake samples at that sampling

site.

Visual inspection and periodic samples were taken between transect lines in order to

record the presence of any species that did not occur at the sampling sites.

The sediment type at each sampling site and the type of shoreline cover at the

beginning of each transect were recorded. A section of shoreline, 50 feet on either side

of the transect intercept with the shore and 30 feet back from the shore, was evaluated.

The percentage of each cover type within this 100’ x 30’ rectangle was visually estimated

and verified by a second researcher.

An Excel file provided by Deb Konkel, DNR Eau Claire, was used to enter and

analyze the data.

71

Bear lake Aquatic Plant Species

Of the 20 species found in Bear Lake three were emergent species, four were

floating leaf species and 13 were submergent species. Chara sp. was the most frequent

species found (59%). While Najas flexilis, Potamogeton zosteriformis and

Ceratophyllum demersum were also abundant (32%, 25%, 19%). Figure 32 lists the

aquatic plant species that were found in Bear Lake during the 2001 aquatic plant survey.

Table 7 displays the percent frequency of two species found in Bear Lake.

Figure 32. Aquatic plant species present in Bear Lake.

Scientific Name Common Name I.D. Code Emergent Species 1) Scirpus validus soft stem bulrush scval 2) Typha latifolia cattail typha 3) Pontederia cordata pickerel weed pocor Floating leaf Species 4) Lemna minor small duckweed lemin 5) Nymphaea odorata white water lily nyord 6) Nuphar advena yellow pond lily nuadv 7) Spirodela polyrhiza(L.)Schleiden.

great duckweed sppol Submergent Species 8) Caltha palustris marsh marigold capal 9) Ceratophyllum demersum coontail cedem 10) Chara sp. muskgrass chara 11) Elodea canadensis Michx. common waterweed elcan 12) Myriophyllum sibiricum Komarov. common water milfoil mysib 13) Myriophyllum spicatum L. Eurasian water milfoil myspi 14) Najas flexilis (Willd.) Rostkov & Schmidt. Slender naiad nafle 15) Potamogeton illinoensis Illinois pondweed popec 16) Potamogeton pectinatus L. Sago pondweed popec 17) Potamogeton richardsonii clasping leaf pondweed poric 18) Potamogeton zosteriformis Fern.

flat-stem pondweed pozos 19) Utiricularia vulgaris bladderwort utvul 20) Vallisaneria americana water celery vaame

72

Table 7. Frequency of Occurrence of aquatic plant species in each depth zone.

0%10%20%30%40%50%60%70%80%90%

100%

Zone1 Zone2 Zone3 Zone4

Depth Zone

Freq

uenc

y of

Occ

urre

nce

mysibchara

73

Coefficient of Conservatism

The Coefficient of Conservatism is the probability that a species will occur in a

relatively undisturbed habitat. Each species is assigned a value from 0-10 (ref). The

average Coefficient of Conservatism is the mean of the Coefficients of Conservatism for

each species found in a lake. The Coefficient of Conservatism has a range from a low of

2.0, the most disturbances, to a high of 9.5, the least disturbed. Bear Lake has an average

coefficient of conservatism of 5.1. This places Bear Lake in the lowest quartile of lakes

in Wisconsin, among the group of lakes in Wisconsin most disturbance tolerant. The

Floristic Quality Index is 22.25, which is below the mean for Wisconsin lakes. This

indicates that plants in Bear Lake are exhibiting the effects of disturbance. Table 8

displays the coefficient of conservatism for species found in Bear Lake.

Table 8. Table of Coefficient Conservatism for species found in Bear Lake.

Coefficient Species Conservatism

Caltha palustris Ceratophyllum demersum 3.00 Chara sp. 7.00 Elodea canadensis 3.00 Lemna minor 5.00 Myriophyllum sibiricum 7.00 Myriophyllum spicatum Najas flexilis 6.00 Nuphar advena 8.00 Nymphaea odorata 6.00 Pontederia cordata 9.00 Potamogeton illinoensis 6.00 Potamogeton pectinatus 3.00 Potamogeton richardsonii 5.00 Potamogeton zosteriformis 6.00 Scirpus validus 4.00

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Total Occurrence

Total occurrence was determined by adding each occurrence of the species

throughout the depth zones. The three species with the greatest total occurrence in Bear

Lake were Chara sp., Najas flexilis, and Potomageton zosteriformis. The two species

with the least total occurrence were Myriophyllum spicatum, Pontederia cordata and

Spirodela polyrhiza. Chara sp. had the highest total occurrence in depth zones one, two,

and three. In depth zone four Ceratophyllum demersum had the highest total occurrence.

Table 9 lists the total occurrence for species found in Bear Lake.

Table 9. Table of Total occurrence for species found in Bear Lake.

Total Species Occur.

Caltha palustris 8.00 Ceratophyllum demersum 19.00 Chara sp. 59.00 Elodea canadensis 5.00 Lemna minor 2.00 Myriophyllum sibiricum 9.00 Myriophyllum spicatum 1.00 Najas flexilis 32.00 Nuphar advena 13.00 Nymphaea ordonata 9.00 Pontederia cordata 1.00 Potamogeton illinoensis 14.00 Potamogeton pectinatus 6.00 Potamogeton richardsonii 6.00 Potamogeton zosteriformis 25.00 Scirpus validus 8.00 Spirodela polyrhiza 1.00 Typha latifolia 5.00 Utricularia vulgaris 2.00 Vallisaneria americana 31.00

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Percent Frequency

The percent frequency of each species was determined by taking the number of

sampling sites at which each occurred divided by the total number of sampling sites. The

species in Bear Lake with the highest percent frequency were Chara sp., Najas flexilis,

and Vallisaneria americana. The species with the least percent frequency were

Myriophyllum spicatum, Pontederia cordata and Spirodela polyrhiza. Table 10 lists the

percent frequency for species of aquatic plants in Bear Lake.

Table 10. Table of percent frequency for species of aquatic plants in Bear Lake.

Species %Freq. Caltha palustris 8.00% Ceratophyllum demersum 19.00% Chara sp. 59.00% Elodea canadensis 5.00% Lemna minor 2.00% Myriophyllum sibiricum 9.00% Myriophyllum spicatum 1.00% Najas flexilis 32.00% Nuphar advena 13.00% Nymphaea ordonata 9.00% Pontederia cordata 1.00% Potamogeton illinoensis 14.00% Potamogeton pectinatus 6.00% Potamogeton richardsonii 6.00% Potamogeton zosteriformis 25.00% Scirpus validus 8.00%

Simpson’s Diversity

The Simpson’s Diversity Index for Bear Lake was 0.89. This number indicates a

very good diversity. A rating of 1.0 would mean that each plant in the lake would be a

different species.

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Total Density

Total density, was determined by adding the total of times each species was found

on a rake sample. The species with the overall highest total density in Bear Lake were

Chara sp., Najas flexilis, and Vallisaneria americana. The species with the least total

density were Typha latifolia, Pontederia cordata and Lemna minor. The species with the

greatest density in depth zone one were Chara sp., Nymphaea ordonata, and Vallisaneria

americana. The species with the greatest density in depth zone two were Chara sp. and

Scirpus validus. In depth zone three Chara sp. and Najas flexilis had the greatest density.

It depth zone four Ceratophyllum demersum had the greatest density. Table 11 shows the

total density of aquatic plant species found in Bear Lake.

Table 11. Table of total density of aquatic plant species found in Bear Lake.

Total Species Density

Caltha palustris 35.00 Ceratophyllum demersum 53.00 Chara sp. 168.00 Elodea canadensis 9.00 Lemna minor 2.00 Myriophyllum sibiricum 9.00 Myriophyllum spicatum 3.00 Najas flexilis 58.00 Nuphar 31.00 Nymphaea ordonata 30.00 Pontederia cordata 2.00 Potamogeton illinoensis 29.00 Potamogeton pectinatus 13.00 Potamogeton richardsonii 13.00

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Mean Density

The mean density of species varied with the depth. Chara sp. was the species

with the greatest mean density for depth zones one through three. As would be

anticipated, Najas flexilis was most dense in zone three and decreased in zone four. The

density of Myriophyllum sibiricum increased slightly in depth zone four, but showed vary

little variation in depth zones one through three. Figure 33 shows the mean density of

three species of aquatic plants in each depth zone of Bear Lake.

Figure 33. Diagram of the mean density of three species of aquatic plants in each depth zone of Bear Lake.

0.0

1.0

2.0

3.0

Zone1 Zone2 Zone3 Zone4

Depth Zone

Mea

n D

ensi

ty

CharaN. milfoilNajas

Dominance Value

Dominance value was calculated by adding the relative frequency and relative

density. The species with the greatest dominance value in Bear Lake were Chara sp.,

Vallisineria Americana, Najas flexilis and Ceratophyllum demersum. The species with

the least dominance value were Lemna minor, Myriophyllum spicatum and Utricularia

vulgaris. Figure 34 shows dominance values for aquatic plant species found in Bear

Lake.

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Figure 34. Diagram of dominance values for aquatic plant species found in Bear Lake.

Najas flexilis

Potamogeton illinoensis

Ceratophyllum demersum

Other Species

Vallisineria americana

Chara

Scirpus validus

Potamogeton zosteriformis

Discussion (S. Nichols, WGNHS and S. Allen)

The aquatic plant community is average quality, but has potential to get worse

with increased nutrient or turbidity inputs and has the potential for milfoil to spread

rapidly. For example if turbidity were to change the pondweeds (Potamogeton spp.),

which are somewhat turbidity tolerant would be replaced with coontail (Ceratophyllum

demersum), sago pondweed (Potamogeton pectinatus), and Myriophyllum spicatum will

become a more dominant part of the vegetaion.

The floristic quality of the lake is below the median on both a regional and

statewide level, which isn’t a concern at this point. The reason for the low floristic

quality is the average conservatism value. It is in the lower quartile of lakes on both a

statewide and regional level. This means that the species in the lake are very tolerant to

disturbance. The two predominant species are Chara and Najas. These are two

pioneering species that usually invade open areas but they are not good competitors.

Usually these species are replaced by others if there is no disturbance which may allow

Myriophyllum spicatum to spread rapidly in open areas.

79

Wisconsin Lakes Modeling Suite (WiLMS) (Amy Dechamps and Paul McGinley)

Background

Hydrologic and phosphorus budgets for Bear Lake were developed using data

collected during the 2001 study and other sources of information. The budgets are useful

for understanding the most significant contributors of phosphorus to the lake and can

thereby assist in lake management. The concentration of phosphorus in the lake is the

result of both external and internal sources of phosphorus. The available phosphorus

determines the level of biological productivity. The biological productivity ultimately

impacts water clarity, plant and animal communities, and oxygen levels.

The hydrologic and phosphorus budgets of this study were developed using data

which were collected over a relatively short time frame and projected to budgets which

are applicable of a longer time period. Year to year variations in flow and phosphorus

loading are expected. This discussion details the assumptions used in making the

hydrologic and phosphorus budgets. As new information is collected or additional

studies are performed, these budgets can be improved.

Hydrology

The sources of water to Bear Lake are surface streams which flow intermittently

into the west side of the lake, precipitation falling directly on the lake, surface water

which runs into the lake from the direct drainage area surrounding the lake, and the

groundwater that discharges into the lake.

Surface water entering the lake includes flow from the streams and runoff from

the direct drainage area surrounding the lake. Historical precipitation and

evapotranspiration from land is approximately 30 inches and 20 inches per year,

respectively, for Waupaca County (Olcott, 1968). The difference, approximately 10

inches per year, is the runoff to streams in the form of surface and groundwater. As

groundwater was directly measured (discussed in a following paragraph), we subtracted

its estimated flow contribution. In the direct drainage area, two inches per year was used

as the total unit runoff largely due to major storm events or snow melt on frozen ground

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because of the relatively permeable soils in Waupaca County. The portion of

precipitation that falls on the lake and is not evaporated was assumed to be 3.8 inches in

Waupaca County (WiLMS, 2001).

Bear Lake has three streams that flow intermittently and converge to one inlet,

which drains into the west end of the lake. Each intermittent stream was measured for

discharge between March and November 2001. Based on discharge measurements in the

study, the composite mean flow of the three streams was 1.0 cubic feet per second (cfs).

The range of inflow when sampled was 0 to 2.1 cfs; higher flows are likely during storm

events. The streams account for surface drainage of approximately 77 percent of the

watershed, and they may also drain a portion of the groundwater recharge area. The area

of the Bear Lake watershed, including stream catchments, is 2720 acres. The area of the

watershed draining directly into the lake is 632 acres.

Groundwater flow to the lake was assayed using mini-piezometers at 69 sites

during the week of August 8 – 14, 2001. The velocity (calculated by Hvorslev’s method,

1951) of all upwelling sites was multiplied by the “upwelling area” assigned to each site

to determine the volume of groundwater inflow into the lake. The upwelling area is the

product of a 35-foot upwelling buffer into the lake [based on work by McBride and

Pfannkuch (1975) and field-testing] and the distance halfway between each upwelling

site and its adjacent sites. This area was calculated in Arc View GIS 3.2a. The volume

of groundwater inflow from each site was then summed for a total groundwater

contribution. The total inflow was entered into WiLMS as a point source for phosphorus.

The calculated groundwater inflow was 1.8 cfs, which constitutes 60 percent of the water

budget.

The estimated flow into Bear Lake from the different components of the

hydrologic budget totals 3.0 cfs. Although the flow is based on several assumptions, it is

similar to the discharge at the stream outlet, which was a median of 1.7 cfs (average 2.2

cfs and ranged from 0.3 to 7.2 cfs). There was one down-welling site on Bear Lake

located at the stream outlet, and the volume of flow leaving through groundwater was 0.1

cfs. Using these values for the hydrologic budget, the water residence time of Bear Lake

is approximately 4 years.

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Phosphorus

The phosphorus in Bear Lake is the result of phosphorus entering the lake from

external sources and internal cycling of phosphorus. External sources include

phosphorus from stream flow, direct drainage, groundwater, and atmospheric deposition.

The Wisconsin Department of Natural Resources’ WiLMS model (WDNR, 2001) was

used to estimate phosphorus loading into Bear Lake for external sources which were not

directly measured. WiLMS (Wisconsin Lake Modeling Suite) uses coefficients for land

uses based on previous research to estimate the amount of delivered phosphorus to a lake.

The intermittent stream inflow to the lake was treated as a point source. Based

on the composite average inflow of 1.0 cubic feet per second and a median stream

phosphorus concentration of 0.07 µg/l, the mass of phosphorus coming into the lake

through this source is 63 kg/yr.

The phosphorus transport from the portion of the watershed that does not drain by

way of the streams was estimated by WiLMS. The watershed was delineated using

USGS 1:24,000-scale topographic maps. The direct drainage area (surface runoff into the

lake) was also delineated and classified according to land use. Land use cover data was

derived using Landsat Thematic Mapper satellite imagery from 1991-1993 and classified

into land use categories (WDNR, WISCLAND). WiLMS manipulated the acreage by a

standard export coefficient for the land use type (based on literature reviews and WiLMS

defaults) to estimate the P loading into the lake. The phosphorus loading from the direct

drainage area is summarized in Table 12, contributing approximately 150 kg/yr of

phosphorus.

The groundwater phosphorus contribution was estimated by assuming a

“background concentration” from all sites but three around the lake. These three sites

exhibited significant levels of P almost certainly due to internal phosphorus loading (sites

had high phosphorus, low chloride, and high ammonium, signs of organic matter

decomposition). Groundwater sample reactive phosphorus concentrations are shown in

Figure 30. The most-likely estimate of P loading from groundwater was determined by

multiplying the inflow volume of each upwelling site by the phosphorus concentration of

that site. The total phosphorus loading from sites considered to have background levels

of phosphorus was 12 kg/yr. Phosphorus loading in groundwater from septic drain fields

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was calculated separately using WiLMS. The septic contribution was estimated

assuming that 85 persons spend 365 days at the lake. This was projected from a survey

conducted of Bear Lake residents. Average phosphorus loadings of 0.3 to 0.5 kg per

person/year and phosphorus retention rates of 60 and 50 percent resulted in phosphorus

loading from septic drain fields of 10 to 21 kg annually (low estimate and most-likely,

respectively). Atmospheric deposition of phosphorus to the lake was assumed to be 0.24

lb/acre/yr (21 kg/yr) taken from WiLMS.

Table 12 summarizes the hydrologic and phosphorus contributions estimated for

Bear Lake. The total phosphorus loading to the lake is estimated to be 175 kg/year (385

lb/year) for a low estimate or 268 kg/year (590 lb/year) as the most likely estimate. This

is the estimated external loading. The phosphorus which leaves the lake was estimated

by measuring the concentration and flow in the stream at the lake outlet. Based on the

median flow of 1.7 cfs and a median concentration of 0.07 mg/L, it is estimated that 107

kg/year (235 lb/year) are leaving the lake through the stream. Mini-piezometer sampling

revealed 2.9 kg/year are leaving through groundwater.

Because a portion of the phosphorus that enters the lake is expected to be retained

by settling in the lake, we anticipate the phosphorus leaving the lake would be less than

that which enters. Although internal sources of phosphorus (e.g., mixing of surface

waters with phosphorus enriched deeper waters during the summer) could increase the

phosphorus leaving the lake, it is likely the phosphorus loading to Bear Lake is

underestimated. One of the more significant sources of uncertainty is the estimate of

groundwater phosphorus contribution to the lake. There was evidence from the mini-

piezometer investigation that some areas of the lake have higher concentrations of

phosphorus.

In-Lake Phosphorus Concentration Modeling

Lake studies since the 1970’s have prompted the development of tools to predict

in-lake P concentrations based on estimates of external loads of phosphorus and physical

characteristics of the lake. The WiLMS model utilizes several of these prediction tools.

The predictions of in-lake phosphorus employing the hydrologic and phosphorus budgets

were compared to calculations of actual data to ensure the models’ usefulness. The

83

external phosphorus load to Bear Lake was estimated to be approximately 590 lb (268 kg)

per year with a range of 385 to 1400 lb (175 to 635 kg). Based on a lake surface area of

194 acres, this is an aerial loading of 3 lb/acre-yr (0.3 g/m2/yr). Using several of the

prediction models in WiLMS, the average predicted in-lake phosphorus is 12 to 30

mg/m3 (Table 13). During the sampling period for this study, Bear Lake had a growing

season average of 24.5 mg/m3 P and a spring overturn concentration of 23.0 mg/L based

on mid-lake samples collected between April 27 and October 18, 2001, at the deep hole

on the lake described previously.

Phosphorus concentration in the lake water may increase by phosphorus transfer

from sediments in the lake. This can occur do to some degree everywhere on the lake,

but is most pronounced under conditions of high pH or low oxygen. In Bear Lake, the

low oxygen conditions in the deeper portion of the lake appear to result in high

phosphorus concentrations as evident in high P concentrations in the hypolimnion. This

may reflect the release of phosphorus deposited in the past, and this phosphorus is only

slowly released and removed from the lake. This phosphorus can transfer into the upper

portions of the lake during overturn, thereby becoming available to the plants and algae.

Table 12. Hydrologic and Phosphorus Load Summary

P Load (kg/yr) Category Area Flow

Low Most-likely

% P Loading

Groundwater 1,607,580 m3/yr 1.8 cfs 12 4.5

Stream Inflow 893,100 m3/yr 1.0 cfs 63 23.3

Septic Tank (85 capita years) 10 21 7.9 Agriculture 240 acres 48 97 36.2 Mixed Ag 75 acres 24 30 11.3 Grass/Pasture 129 acres 5 16 5.9 Rural Residence

43 acres 1 2 .6

Wetlands 44 acres 2 2 .7

Direct Drainage Area

Forest 101 acres

.15 cfs

2 4 1.7 Lake Surface/Atmospheric Deposition (Lake Surface Area) 194 acres .08 cfs 8 21 7.9

Total 3.0 cfs 175 kg/yr

268 kg/yr 100%

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Table 13. Calculated and Predicted Values

Hydraulic Residence Time 4 years (volume/outflow)

P Loading 175 – 268 kg/yr

TP observed 24.5 µg/L

TP predicted in WiLMS 16-30 mg/m3

12-22 mg/m3

16-30 mg/m3

Walker, 1987 Reservoir

Rechow, 1979 General

Rechow, 1977 water load <50m/yr

Uncertainty

As with any modeling and fieldwork, there are uncertainties in the estimates of

the phosphorus loading. The streamflow estimates are based on measurements taken

with the Marsh McBirney flow meter about every month. Sampling dates do not

correspond for each site. The quantity of water as well as the quality has limited

sampling data. Water quality samples of the stream inflow are based on an average of

four samples taken during the spring months. Mini piezometers give an indication of the

velocity and quality of the groundwater for one point in time. This data is also used with

caution as it may vary with season and over longer time periods as groundwater levels

rise and fall. In 2001, the groundwater levels were lower than the long-term average for

this area (USGS, 2002) and would decrease the groundwater flow into the lake.

The soil types in Waupaca County are generally sandy, and water infiltrates

readily. For this reason, the default coefficients used to estimate loading for agriculture

may be high. Phosphorus travels in the sediments carried by surface water and may not

reach the lake if retained by the soils. As a result, the lower phosphorus loading values

were considered a more accurate estimate of the phosphorus content in the lake.

Lastly, the spring overturn during the year of 2001 is not believed to have

completely mixed. Therefore, the water quality estimate may not reflect the in-lake

phosphorus.

85

Conclusions/Recommendations

1. Water moves to Bear Lake via streamflow, direct precipitation, surface runoff, and groundwater. Pollutants and other contaminants can enter the lake directly through these processes.

2. At depths below 20 feet, the dissolved oxygen in the water drops below 1 mg/L

during much of the growing season, making much of the water inhospitable for most organisms. These anoxic conditions also allow complex reduction reactions to occur in the hypolimnion.

3. Sources of nutrient inputs (nitrogen and phosphorus) to Bear Lake come from

within the watershed and from localized land use practices, therefore, efforts to reduce nutrient inputs to the lake should be made by both shoreland residents and landowners within the watershed.

4. Several times during the year total phosphorus concentrations exceeded 0.030

mg/L. Above this concentration stimulation of algae blooms and aquatic plant growth occurs. Average total phosphorus concentrations in Bear Lake are greater than the average for natural lakes in Wisconsin, however, much of this phosphorus likely entered the lake years ago and continues to cycle within the system. In the past, several barnyards around Bear Lake and within its watershed contributed large quantities of nitrogen and phosphorus to the lake. Once in a lake, phosphorus is slow to leave the system so it will some time before significant improvement in water quality can be observed.

5. In 2000-01, chlorophyll a concentrations were lower than concentrations in

samples acquired in 1980-82. The same is true for most of the total phosphorus samples acquired in 2000-01. Continued water quality monitoring is recommended to determine if this is a trend or year-to-year variation.

6. The WiLMs model suggests that about 40% of the phosphorus inputs to the lake

are from agricultural sources. Best management practices should continue to be implemented to further reduce these inputs.

7. Shallow groundwater samples contained nutrients and chloride, likely from local

land use practices. These nutrients should be reduced or eliminated whenever possible. New septic drainfields should be sited as far from the lake as possible.

8. Ninety-five percent of the landowners responding to the survey indicate they use

lawn fertilizer. Efforts should be made to eliminate/reduce the use of these fertilizers. Soil sampling should be conducted routinely to determine if any fertilizer application is warranted. Use of native plants eliminates the need for fertilizer application.

86

9. Existing buffered riparian areas around the lake should be protected. Much of the developed part of the lake lacks sufficient buffers to remove sediments and nutrients from runoff and to provide habitat for plants and animals. Buffers should be re-established in these areas, and should include grasses, forbs, shrubs, and trees. Current Waupaca County Shoreland Protection laws state that the vegetation protection area is within 50 feet of the ordinary high water mark. Land disturbing activities and vegetation removal are prohibited in this area, however, some exceptions exist including a 30 foot view corridor. Details regarding these exceptions can be found in Appendix G.

10. Many of the residences around the lake have lawns mowed to the water’s edge.

Implementing shoreland buffers will reduce nutrients that enter the lake via surface runoff. This practice would also be consistent with the Waupaca County Shoreland Zoning Ordinance.

11. Areas of minimal/no development should be protected when possible. These

areas are providing spawning habitat for fish, frogs, turtles, and other lake/near-lake inhabitants. Many local, state, and federal programs are available to assist.

12. The aquatic plant survey revealed the presence of Eurasian water milfoil, an

aggressive exotic plant. Currently it is localized so, aggressive action should be taken to eliminate this plant. This plant spreads rapidly; once it spreads it is very costly to manage and cannot be eliminated.

13. The diversity of aquatic plants in Bear Lake is about average for this area of

Wisconsin. Most of the plants that are present are tolerant of disturbance and some are quite tolerant of light-limited conditions (i.e. algae blooms). These plants may become a nuisance if frequency of algae blooms increases.

14. Aquatic plants in shallow water provide habitat for aquatic organisms and help to

buffer the impact of waves on the shoreline, thus reducing erosion and the need for rip-rap. Efforts should be made to minimize removal of near shore aquatic plants.

15. Many of the conclusions and recommendations from this study are similar to

those recommended from the 1980’s study on Bear Lake, therefore, the recommendations from the previous study are included in Appendix F. Though many advancements have been made, these management recommendations and conservation ideas should continue to be implemented and followed.

16. A management plan should be developed and should include a vision and goals

for the lake. It should identify ways to achieve these goals and should be incorporated into the Town plans where appropriate. Many people should be involved in this process and inclusion of local and state professionals is encouraged.

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APPENDICES

88